Wednesday, December 26, 2012

CBSE solved Questions Chapter - 15 Our Environment Class - X Biology

Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Removal of all the organisms of a trophic level will affect the entire ecosystem of that area. Its impact on different trophic levels will be different because of the organisms of a trophic level are directly dependent on them while the organisms of other trophic level are indirectly depend on them for their food. For example, killing of herbivores will increase the number of carnivores and killing of carnivores will increase the number of herbivores. Most of the organisms will die of starvation.
How do flows of energy occur in tropic level?
Energy is used and conveyed from one trophic level to another is a food chain. This is called flow of energy. Green plants capture about 1% of the solar energy during photosynthesis. A part of this trapped energy is used by plants in performing their metabolic activities and some energy is released at heat into the atmosphere. The remaining energy is chemical energy stored in the plants as ‘carbohydrates’.
                                 When plants are eaten up by herbivores, the chemical energy stored in the plants is transferred to these animals. These animals (herbivores) utilize some of this energy for metabolic activities, some energy is released as heat and the remaining energy is stored.
What are the characteristics of energy transfer in the biosphere?
The following are the characteristics of energy transfer in the biosphere:
(i) Energy is supplied by the sun and it is not created in the biosphere. Energy is only converted from one form to another in the biosphere.
(ii) There is a continuous transfer of energy from one trophic level to the next in a food chain.
(iii)At each trophic level, some of the energy is utilized by the organisms for their metabolic activities.
(iv)  At each trophic level, some amount of energy is utilized for the composition of decomposers.
(v) At each trophic level, there is loss of energy, which goes into the environment and remains un-utilized.
(vi) At each trophic level, the amount of energy available is less than that available at the previous level.
Why is energy flow considered as unidirectional?
The flow of energy is unidirectional and non cyclic. The energy captured by the autotrophs does not return to the sun, and the energy which passes to the subsequent levels does not come back to autographs. The amount of energy goes on successively decreasing from the producers to the carnivores.
How much energy is lost in transferring from one trophic level to other in a food chain?
Ans.  90%.
What is biomass?
The amount of organic matter present in an organism is called biomass.
What will happen if we kill the organisms in one trophic level?
The balance in ecosystem will be disturbed because in an ecosystem every trophic level is interlinked with the other. Thus, absence of any one trophic level will surely create problems for the other trophic level dependent on the previous one.
Define biomagnifications.
The increase in concentration of a chemical per unit weight of the organisms with successive rise in trophic level is called biomagnifications.
How does a food web an important factor of our environment? Describe its four benefits.
Importance of food web
(i) Starvation: Food web does not allow any population to starve when members of lower trophic level decrease in number.
(ii) Checking Overpopulation: Food web does not allow a species to overgrow as increased availability will increase the chance of higher number of its predations.
(iii) Endangered Population: It allows endangered population to grow in size.
(iv) Stability: Food webs provide stability to ecosystems.
What is 10% Law?
The energy available at each successive trophic level is only 10 percent of the previous level.
How much energy will be available to hawks in the food chain comprising hawk, snake, paddy and mice, if 1,000 J of energy is available to wheat plants from the sun?
Wheat plants represent the producer level. They trap only 1% of the sun’s energy falling on them. So, the energy available in wheat will be 1% of 1,000 J which will be 10 Joule. We can now show the food chain and apply ten per cent law to it.
Wheat plant (10J) --10%--> Mice (1J)---10%---->Snake(0.1J)--10%-->Hawk(0.01J)
Thus, the energy available to the hawk will be 0.01 J.
Differentiate between food chain and food web?
Food chain                                                                             
1. Food chain consists of a single series of food relations.
2. It has maximum 4-6 trophic levels of different species.
3. Each organism uses a particular food.
4. Starvation is observed whenever the members of lower trophic level decrease in number.
Food web
1. Food web is a complex network of several series of food chains or food relations.
2. It has a number of trophic levels or populations of different species.
3. Each organism can use different types of type of food.
4. Food webs do not allow starvation and help in increasing the population of endangered species.
Why is damage to the ozone layer a cause of concern? What steps are being taken to limit this damage?
 Ozone layer has become a cause of concern because depletion of ozone layer can cause serious effects on human body and other organisms of the environment like —
(i) Cancer in human beings.
(ii) Loss of immunity in humans.
(iii) Destruction of aquatic life and vegetation.
(iv) Temperature changes and rainfall failures.
Steps being taken to reduce it are :
(i) by reducing the use of CFCs — Many countries have already banned the use of CFCs.
(ii) by developing substitutes of CFCs — Scientists have already developed some substitutes which are ozone-friendly.
Which compounds are responsible for the depletion of ozone layer?
 Ozone depleting substances like chlorofluorocarbons, hydrocarbon, N2O, chlorine, etc. are responsible for the depletion of ozone layer.
Which disease is caused in human being due to depletion of ozone layer in the atmosphere?
Ozone layer is located in the atmosphere as a part of stratosphere. Skin cancer is caused in human being due to depletion of ozone layer in the atmosphere
Why is ozone layer getting depleted at higher levels of the atmosphere?
 Due to the release of CFCs in the environment the ozone layer is getting depleted at higher levels of
How is ozone formed in the upper atmosphere? Which compounds are responsible for the depletion of ozone layer?
The ozone layer occurs naturally in the stratosphere. The ozone layer is formed when intense UV radiation from the sun reacts with ordinary molecules of oxygen (O2) in the stratosphere to dissociate into single oxygen atoms (O). Single oxygen atoms are very reactive they combine with O2 to form O3.
The CFCs (chlorofluorocarbons), halons, nitrous oxide, methane, carbon tetrachloride and chlorine are responsible for the depletion of ozone layer.
When is World Ozone Layer Preservation Day celebrated?
World Ozone Layer Preservation Day is celebrated on September 16.
What is green house effect?
The gases like CO2 and methane absorb infra red radiations of the sun and cause heating of the earth. It is known as green house effect.
Suggest activities in our daily life which are eco friendly.
 (i) Cloth bags should be used in place of plastic bags or polythenes.
(ii) Domestic wastes and kitchen wastes can be made use of as manures or compost for plants.
(iii) We should reduce the wastage of foods, water, or any other thing.
(iv) We should not use the electronic equipments using the ozone depleting gases or chemicals.
(v) From biodegradable waste, biogas can be prepared which costs much less than other fuels.
(vi) Separation of biodegradable and non-biodegradable wastes of our house.
How can you help in reducing the problem of waste disposal? Give any two methods.
Every individual should play a role in reducing the problem of waste disposal. They can do that by-
(i) Improved packing methods.
(ii) Increased use of disposable items.
(iii) Use of compost in the field
What is the importance of phytoplankton?
The phytoplankton supply dissolved oxygen to the organisms living in water. They are food for fish.
Which pollutants are contributed by airplanes?                              
Aerosols  and CO2.
How is ozone layer formed in the atmosphere? What is the function of this layer?
The ozone layer occurs naturally in the stratosphere. The ozone layer is formed when intense UV radiation from the sun causes ordinary molecules of oxygen (O2) in the stratosphere to dissociate into single oxygen atoms (O). Single oxygen atoms are very reactive and combine with O2 to form O3.
O2 + UV radiation O + O
O + O2  O3 (ozone)
Function: Ozone absorbs UV radiation from the sun, thus shielding the earth’s surface from the harmful effects of this radiation e.g.: skin cancer. 
 Chapter 15 Our Environment solved Questions Download pdf File 
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Monday, December 24, 2012

CBSE_NCERT Chapter 11 Human Eye and Colorful World class 10th

Gist of Lesson for Quick Revision (By JSUNIL)
1. An eye is the most important organ of the human body. It is associated with vision and acts as a vital optical instrument.

2. An eye is spherical in shape of about 2.3 cm diameter and is covered externally by a hard thick and opaque layer called Sclerotica. The outermost layer of the eye is sclerotic that protects and holds the eye.

3. Cornea is transparent part bulging out of eye and allows the light to enter in the eye. Cornea is also known as the window or aperture of the eye.

4. Iris is a circular diaphragm having a hole in its centre .this hole is called pupil

5. Iris has muscles and coloured pigments that provide different colour y eyes

6. Iris controls the amount of light entering the eye through the pupil.

7. The pupil becomes small when bright light falls on the eye. However, it becomes wide when there is dim light.

8. The eye lens is a crystalline convex lens made up of transparent and flexible tissues behind the pupil and held by the muscles called ciliary muscles. It focuses inverted the images of objects on the retina of the eye.

9. Ciliary muscles control the focal length of the eye lens by contracting and relaxing. This ability

10. When ciliary muscles contract lens become thin thus the focal length of the lens increases. 

11. When ciliary muscles expand lens become thick, and decrease the focal length of the lens. This helps us to see nearby objects clearly.

12. The ability of the eye lens to adjust its focal length is called accommodation.

13. The focal length of the eye lens cannot be decreased below a certain minimum limit this is why a normal eye not able to see clearly the objects placed closer than 25 cm.

14. The image distance in the eye remains same when we increase the distance of an object from the eye as distance between eye lens and retina is constant.

15. The least distance of distinct vision for a young adult with normal vision is about 25 m. it is called near point

16. The furthest distance of distinct vision for a young adult with normal vision is at infinity. it is called far point.

17. The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to accommodation.

18. A normal eye can see objects clearly that are between 25 cm and infinity.

19. In old age eye lens of people becomes milky and cloudy. This condition is called cataract. This causes partial or complete loss of vision. It is possible to restore vision through a cataract surgery.

20. One eyes of human being has a horizontal field of view of about 150° So for  a horizontal field of view of about 180° We have two eyes.

Sunday, December 23, 2012

Problem Solving Assessment:Sample Question Paper


PictureEnglish Language    PSA ENGLISH    
(Questions 1 to 8) Read the following passage carefully and select the most suitable option from  each list according to the corresponding  number in the passage
The Indian Peafowl, alternatively(1) known as the Blue Peafowl, is the national bird of India.  The male is called a peecok(2) and has  feathers which are made up of a range(3) of beautiful colours.  The female is  called a peahen.   The majority(4) of the female’s feathers are a plain (5)brown colour. These birds usually  live in sparsely  populated areas such as forests and don’t fly very often.  They eat berries, seeds and  sometimes snakes or small animals.

Q 1.  Which of the following could replace ‘alternatively’ as  used  in the passage above?
1) and
2) also
3) then
4) never

Q 2.    Which of the following is the correct spelling of ‘peecok’?
1) peacok
2) peacock
3) peecock
4) peakock

Q 3.   Which of the following could replace ‘a range of’ as used in the passage above?
1) pretty
2) unusual
3) a group of
4) a selection of

Q 4.    Which of the following is the opposite in meaning to ‘majority’ as used in the passage above?
1) lots
2) several
3) nearly all
4) not many 3

Q 5.   Which of the following could replace ‘plain’ as used in the passage above?
1) pale
2) dark
3) simple
4) gentle

Q6.   Which of the following could replace ‘sparsely’ as used in the passage above?
1) lightly
2) heavily
3) densely
4) narrowly

Q 7.  Which of the following could replace ‘populated’ as used in the passage above?
1) popular
2) settled
3) liveable
4) uninhabited
Q8.   Which of the following could replace ‘They’ as used in the passage above?
1) People
2) Hunters
3) Animals
4) Peafowl

(Questions 9 to 12)This passage contains errors and an omission. Choose the correct option from the lists  below to correct these errors and complete the passage.

The commonwealth Games were held in India in 2010. (9)
It was very successful and the attendances were high.  10)
A village was built for the athletes besides the stadium.       (11)
During an interview, the TV commentator  said,_______________________(12)

Q9
1) Comma required after ‘Games’.
2) ‘Games’ should not begin with a capital.
3) Capital letter required for ‘commonwealth’
4) Apostrophe required after ‘commonwealth’4

Q10
1) They are
2) They was
3) They were
4) They been
Q11
1) near
2) close
3) inside
4) toward

Q12
1) These were the best games ever.
2)   “These were the best games ever!” 
3) “These were the best games ever”!
4) “that these were the best games ever.”

(Questions 13 to 16) In this passage, errors or parts of a sentence which have been left out, have been  underlined.  To correct these errors and correctly complete the passage, choose the correct option  from the lists below.

Bina the zookeeper woke early although she wanted to see the tiger     (13)
give birth. The zoo vet were hoping  that the event would be                  (14)
successful and had stayed with the tiger overnight. When he arrived    (15)
at work, the excitement was already beginning to build      ______ .       (16)

Q13.
1) because
2) however
3) therefore
4) as a result of

Q14.
1) will hope
2) is hoping
3) had hoped
4) was hoping5

Q15.
1) she
2) they
3) the vet
4) the man

Q16.
1) because there was a new cage for the tiger.
2) as it seemed that the cub’s arrival was close.
3) when the tiger cub went to the pond to have a drink of water.
4) since the sun was shining and it was a joyful day for everyone.

( Questions 17 to 20) Complete this passage by selecting the most suitable option from the list for  the corresponding gap.

Dieticians claim that to maintain a healthy body, we __(17)__ to stay away from high calorie foods.
But selecting low calorie nutritious foods __(18)__ quite a daunting task. Selecting food, studying nutrition facts on food labels and preparing meals all seem to add to the  feeling that healthy eating is __(19)__. Another barrier to healthy eating is the marketing of cheap,    pre-packaged foods  that has made it so  much easier to reach out for a __(20)__ snack.
Q17.
1) may try
2) should try
3) might have tried
4) would have tried
Q18.
1) can be
2) should be
3) may have been
4) would have been
Q19.
1) a simple effort.
2) easily achievable.
3) urgently required.
4) a demanding task.6
Q20.
1) cheap low calorie
2) simple and natural
3) tempting unhealthy
4) pre-packaged healthy

( Questions 21 to 24) Complete this passage by selecting the correct option from the list for the  corresponding gap.

Bankim Chandra Chatterjee was one of the greatest novelists and poets of India. He is __(21)__ for  being the author of Vande Mataram, the National Song of India.  Chatterjee began his ( Questions 21 to 24) Complete this passage by selecting the correct option from the list for the  corresponding gap.  Bankim Chandra Chatterjee was one of the greatest novelists and poets of India. He is __(21)__ for  being the author of Vande Mataram, the National Song of India.  Chatterjee began his __(22)__ career  as a writer of verse, but __(23)___ turned to writing fiction. Bankim Chatterjee was a superb story-teller  and he enjoyed universal popularity. His novels have been __(24)__ into almost all of the major  languages of India.
Q21.
1)   blessed
2)  splendid
3)   infamous
4)   acclaimed
Q 22.
1) prior
2) literary
3) life long
4) song writing
Q 23. 
1) later
2) prior
3) firstly
4) meanwhile
Q 24.
1) reworded
2) translated
3) explained
4) paraphrased__
Download full paper by CBSE 

CBSE/NCERT Board Solved Questions class X NCERT Ch. Periodic Classification

 Solved Questions Set-01
Q.1. Why does silicon is classified as Metalloid?

Ans: Silicon is gray color solid at room temperature with very high melting point and boiling point that lose or gain 4 electrons 3s2, 3p2] having both metallic and non metallic properties so it is classified as Metalloid eg. Sio2
Q.2.Why inert gases have zero valencies?

Ans: It is because Inert gases have 2 or 8 electrons in valence shell.

Q.3. How is valency of an element determined?

Ans: The valency of an element measures its ability to combine with other elements. The valency is determined by knowing place in periodic table.. All the elements in group VIII have eight electrons in their outer shells, and thus have a valency of zero (highly stable). Elements in group I just have one valence electron in their outer shells and thus have a valency of one.

Q.4. why could no fixed position be given to hydrogen in Mendeleev’s Periodic table?

Ans: Hydrogen placed in the first column above alkali metals. it is because hydrogen and alkali metals have similar properties.
However, hydrogen also resembles halogens. Like halogens, hydrogen is a gas, and exists as a diatomic molecule (H2). It forms covalent compounds like halogens unlike alkali metals. Hence, it can also be placed above the halogen group .Therefore, Mendeleev was not able to explain the position of hydrogen.

Q.5. In modern periodic table, the isotopes of Chlorine Cl-35 and Cl-37 having different atomic masses will 
be kept in different slots or they would be assigned same position on the basis of their chemical properties? Give reason in support of your answer

Ans: It is because periodic table is based on the atomic numbers of the element and both the isotopes of chlorine have the same atomic number (Z = 17).

Q.6. Why was Dobereiner’s system of classification of elements into triads not found to be useful?

Ans: it is because he could not arrange all elements in triads.

Q.7. Oxygen (O, 8) and sulphur (S, 16) belong to group 16 of the periodic table :-
(i) Write the electronic configuration and valency of these two elements?
(ii) Which among these will be more electronegative? Why?

Ans: (i) Oxygen (O, 8) = 2,6  ; Vacancy =2           Sulphur (S, 16) = 2,8,6 ; Vacancy =2  
(ii) Oxygen will be more electronegative due to electro negativity decreases from top to bottom because atomic size increases.

Q.8. How does electronic configuration of atoms change in a period with increase in atomic number?

Ans. On moving across a period from left to right, the atomic number of the elements increases, therefore, the number of electrons in the valence shell increases from 1 to 8, i.e, the first element in the given period will have one electron in its valence shell and the last element in the same period will have eight electrons.

Q.9. What happens to the melting points and boiling points of elements while moving down in a group?

Ans. The melting points and boiling points decrease while moving down in group of metals.
The melting points and boiling points increases while moving down in group of non-metals.

Q10. Why Chlorine (atomic number 17) is more electronegative than sulphur (atomic number 16)

Ans: The nucleus of chlorine has more tendency to attract an extra electron than the nucleus of sulphur because chlorine needs only one 1 electron to complete its shell. Hence, chlorine is more electronegative than sulphur.

 Solved Questions Set-02

1. How does the electronic configuration of an atom relate to its position in the Modern periodic table?

Ans. The outermost electron in  electronic configuration give idea of group in Modern periodic table and also period.

2. Give examples of some :  a. Metalloids b. Alkali metals c. Halogens d. Alkaline Earth metals e. Nobel gases or inert elements

Ans: a. Metalloids – Boron, Silicon, Germanium
b. Alkali metals – Sodium, lithium, Potassium
c. Halogens – Fluorine, Chlorine, Bromine
d. Alkaline Earth metals – Magnesium, Calcium
e. Nobel gases or inert elements – Helium, Neon, Krypton

3. How were the positions of different isotopes decided in modern periodic table? 

Ans: All the isotopes of an element have same atomic numbers. In modern periodic table, the elements have been allotted places based on their atomic numbers. Therefore, all the isotopes of an element have been assigned the same position in the modern periodic table

4. Where do you think hydrogen should be placed in the modern periodic table?

Ans: The modern periodic table is based on the atomic numbers of the elements and also upon their electronic distribution. Alkali metals as well as hydrogen have one electron in their valence shell. Therefore, hydrogen should be placed in the group of alkali metals. However, it has been assigned a separate position and is not a member of the group of alkali metals since it is a non-metal.

5. How were the positions of the elements Co and Ni resolved in the modern periodic table?

Ans: On the basis of atomic masses, Ni (58.7) should be placed before Co (58.9). This was defect in Mendeleev’s table because the element Co was placed before Ni. However, the atomic number of (Co = 27) is less than that of Ni ( 28). Therefore, they have been correctly arranged in the modern periodic table.

6. The two isotopes of chlorine have atomic masses 35 u and 37 u. Should they be placed in same slot in the periodic table?

Ans: Yes, they should be placed in the same slot because periodic table is based on the atomic numbers of the element and both the isotopes of chlorine have the same atomic number (Z = 17).

7. Which element is bigger in size, lithium (Z = 3) or Sodium (Z = 11) and why?

Ans: Lithium (Li) atom has only two shells K and L in it whereas a sodium (Na) atom has three shells K L and M. Since a sodium atom has one mote shell than a lithium atom, therefore sodium atom is bigger in size.

8. What were the criteria used by Mendeleev in creating his periodic table?

Ans: Ans. Mendeleev’s periodic table was based on the observation that properties of the elements are a periodic function of their atomic masses. This means that if elements are arranged in the increasing order of their atomic masses, then elements with similar properties get their place in the same group in a successive increasing order of atomic masses.

9. Why did Mendeleev leave some gaps in his periodic table?

Ans. Mendeleev left gaps in his periodic table to keep the elements with similar properties together if predicted. New elements would be discovered later and they would occupy those gaps.

10. Why did Mendeleev treated the hydrides and oxides of element as the basic properties  of elements for their classification?

Ans. During the period when Mendeleev gave his periodic table atomic numbers and electronic configurations were not known. Comparison of properties of elements could be best done by comparing their compounds. He selected oxides and hydrides because oxygen and hydrogen form compounds with most of the elements due to their high reactivity.

11. Why are the elements in the same group of the periodic table show close resemblance in their chemical behavior?

Ans: The chemical properties depend upon the number of valence electrons of an element. The elements in the same group of the periodic table show close resemblance in their chemical behavior as they have same number of valence electrons.

12. What happens to atomic radii in a group and period and why?

Ans: Atomic radius is the distance between the centre of atom and the outermost shell.

In a period, atomic radius generally decreases from left to right.

In a period there is a gradual increase in the nuclear charge. Since valence electrons are added in the same   shell, they are more and more strongly attracted towards nucleus. This gradually decreases atomic radii.

Atomic radii increase in a group from top to bottom.

As we go down a group the number of shells increases and valence electrons are present in higher shell and the distance of valence electrons from nucleus increases. Also, the number of filled shells between valence electrons and nucleus increases Both the factors decrease the force of attraction between nucleus and valence electron. Therefore, atomic size increases on moving down a group.

13. Why are the ionization energy of elements increases in a period from left to right.

Ans: The minimum amount of energy required to remove an electron from a gaseous atom in its ground state to form a gaseous ion is called ionization energy.
The ionization energy increases in a period from left to right. This is because the force of attraction between valence electron and nucleus increases in a period from left to right.

14. What do you mean by Electron affinity: How it is vary in group and periods in modern periodic table?

Ans: The tendency of element to gain an additional electron. This ability is measured by electron affinity. It is the energy change when an electron is accepted by an atom in the gaseous state. Electron affinity is assigned a positive value when energy is released during the process. Greater the value of electron affinity, more energy is released during the process and greater is the tendency of the atom to gain electron.
In a group, the electron affinity decreases on moving from top to bottom as less and less amount of energy is released.
In a period, the electron affinity increases from left to right, as more and more amount of energy is released

15. What do you mean by Electro negativity?

Ans: Electro negativity is relative tendency of a bonded atom to attract the bond-electrons towards itself. It just compares the tendency of various elements to attract the bond-electrons towards themselves.
Electro negativity decreases in a group from top to bottom. Electro negativity increases in a period from left to right. Electro negativity is related to ionization energy. Electrons with low ionization energies have low electro negativity because their nuclei do not exert a strong attractive force on electrons. Elements with high ionization energies have high electro negativity due to the strong pull exerted on electrons by the nucleus.

Solved Questions Set-03

VERY SHORT ANSWER TYPE QUESTION (1 MARKS)

1. In the modern periodic table which are the metals among the first ten elements.

Ans. Only lithium, beryllium.

2. By considering their position in the periodic table which one of the following elements would you expect to have maximum metallic characteristic? Ga, Ge, As, Se, Be.

Ans. Ga.

3. Which of the following statement is not correct statement about the trends when going from left to right across the periods of periodic table.
A. The element becomes less metallic in nature.
B. The number of valence electron increase.
C. The atoms lose their electron more easily
D. The oxide becomes more acidic

Ans. The atoms lose their electron more easily.

4. Element X forms a chloride with the formula XCl2 which is solid with a high melting point. X would most likely be in the same group of periodic table as (a). Na (b). Mg (c). Al  (d). Si?

Ans. (b). Mg

5. Which element has two shells, both of which are completely filled with electrons?

Ans. Ne (2,8).

6. The electronic configuration 2, 8, 2 ?

Ans. Mg (2,8,2).

7. A total of three shells, with four electrons in its valence shell?

Ans. Si (2,8,4).

8. A total of three shells, with three electron in its valence shell?

Ans. Al(2,8,3).

9. Twice as many electrons in its second shell as in its first shell?

Ans. C (2,4).

10. Nitrogen(atomic number=7) and phosphorus(atomic number=15) belong to same group-15 of the periodic table. Write the electronic configuration of these two elements. Which of these two will be more electronegative? Why.

Ans. Electronic configuration of N (7) = 2, 5 Electronic configuration of P (15) = 2, 8,5 
Nitrogen will be more electronegative due to electro negativity decreases from top to bottom because atomic size increases.

11. In the modern periodic table Ca (At no. = 20) is surrounded by elements with atomic number 12, 19, 21, and 38. Which of these have physical and chemical properties resembling Ca.

Ans. 38,12

VERY SHORT ANSWER TYPE QUESTION (2-marks each)

Q.1. Did Doberenier‘s triads also exist in the column of Newland octaves. Compare and find out.

Ans. Yes, Li, Na, K

Q.2. What are the limitation of Dobernier‘s classification?

Ans. Only few elements are classified into triads. So, this classification is rejected.

Q.3. What are the limitations of Newlands law of Octaves

Ans. (a) It was applicable only upto atomic mass 40 of Ca. (b) Two elements Ni and Co are placed in column as F, Cl, Br which have different properties.

Q.4. Use Mendeleev‘s periodic table to predict the formula for the oxide of following element K, C, Ba, Al

Ans. K –I A –K2O C -IV A –CO2 Al –III A-Al2O3 Ba –II A –BaO

Q.5.Besides Ga, which other elements have been discovered that were left by Mendeleev in his periodic table (Any two)?

Ans. Eka-Boron-Scandium Eka-Silicon-Germanium

Q.6. What were the criteria used by Mendeleev in creating his periodic table?

Ans. Two criteria used by Mendeleev (i) Atomic mass   (ii) Similar chemical properties

Q.7. Why do you think the noble gases are placed in a separate group?

 Ans. These gases were discovered very late and placed in a separate group because they were inert.

Q.8. Name two elements you would expect to show chemical reaction, similar to magnesium. What is the  basis for your choice?

Ans. Ca, Be On the basis of the elements belong to same group-2. So valance electrons are same.

Q.9. (a) What property do all elements in the same column of the periodic table as Boron have in common
        b) What property do all elements in the same column of the periodic table as Fluorine have in common?

Ans. (a)  All elements in the same column as Boron have 3e- in valence shell and form oxide X2O3.
       (b)  All elements in the same column as Fluorine have 7e- in valence shell so their valency is one.

Q.10. An atom has electronic configuration 2,8,7 (a) What is the atomic no. of this element? (b) To which of the following elements would it be chemically similar N(7) F(9) P(15) Ar(18)

Ans. (a) Atomic no=17 (b) F(9).

Short answer type question (3-marks each)

Q.1-How could the modern periodic table remove various anomalies of Mendeleev’s periodic table?

Ans-Various anomalies are removed in following ways-

(a) The position for all isotopes of an element justified since they have same atomic number.
(b) The position of certain elements which are earlier misfit like Co-58.9 is placed before Ni-58.7 are now justified because Co has lower atomic number than Ni.
(c) Cause of periodicity explained due to same electronic configuration repeated after certain gap.

Q.2- Name
(a) three elements that have a single electron in their outermost shells.
(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outermost shell.

Ans- (a) Li ,Na ,K(Group-1)
        (b Be ,Mg (Group-2) 
       (3) Ne ,Ar, Kr (Group-18)

Q.3- (a) Li,Na,K are all metals that react with water to liberate H2 gas .Is there any similarity in the atoms of these elements.
(b) Helium is an unreactive gas and Neon gas is a gas of extremely low reactivity, what do their atoms have in common.

Ans-(a) there are following similarities.
(1) these atoms have same number of electrons in outermost shell   3Li -2,1 11Na-2,8,1 19K-2,8,8,1
(2) Li,Na,K react with oxygen to form oxide which are basic in nature.  
(b) both He and Ne have completely filled shell

Q.4-The position of three elements A,B and C in the periodic table are shown below

Group-16
Group-17
           -
-
          -
A
          -
-
          B
C
 (a) State whether A is a metal or non-metals. 
 (b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size then B.       
(d) Which type of ion, cat ion or anion will be formed by element A

Ans-(a)-Non-metal
(b) A is more reactive due to small size, have more tendency to accept outside electron
(c) C is smaller in size than B due to atomic size decreases from left to right in a period
(d) Anion formed due to tendency to accept electron

Q5. How are the positions of elements related to their atomic number in the Modern periodic table?

Ans. The number of valence electrons present in an atom of an element is equivalent to  the group number, while the total number of shells give the period number in which the element to present.
e.g.  1. Atomic no. of Mg=12 ;  Electronic configuration=2,8,2     therefore, Group. no.=2 or IIA   Period no.=3 e.g. 2. Atomic no. of Cl=17; Electronic Configuration=2,8,7       therefore, Groupp. no.=17th  or VIIA

Solved Questions Set-04

Q1. What is Modern periodic Law?

Ans. The Properties of elements are a periodic function of their atomic number.

Q2. What were the limitations of Dobereiner Law of triads?

Ans. Dobereiner could identify only 3 triads from the element known at that time. Hence, this system is not useful.

Q3. State Newlands’s law of Octaves.

Ans. Newland arranged the elements in the increasing order of the atomic masses and found that every eight element had properties similar to that of the first like the notes of music.

Q4. What were the limitations of Newlands’s Law of Octaves?

Ans. 1. It was only applicable only up to Calcium as after Calcium every eighth element did  not posses , properties similar to that of first.

2. At a few places unlike elements were put together like cobalt and nickel along with F, Cl and Br.

Q5. Which 2 criteria did Mendeleev used to classify elements in his periodic table?

Ans. Atomic mass and similarity in chemical property.

Q6. State Mendeleev’s periodic law.

Ans. Properties of elements are a periodic function of their atomic masses.

Q7. Why did Mendeleev leave gap in his periodic table?

Ans. Mendeleev place elements with similar properties one below the other leaving gap  for yet undiscovered elements.

Q8. Name the elements which have since been discovered that were left by Mendeleev  in his Periodic Table?
Ans. Eka Boron – Scandium             Eka   Al - Gallium         Eka   Si - Germanium

Q9. What are the limitations of Mendeleev's periodic table?
Ans.
1. Position of Isotopes was not clear in his table.
2. Wrong Order of atomic mass of certain elements  – Elements with higher atomic  mass were placed before elements having lower atomic mass.    e.g. Cobalt was placed before nickel.
3. Position of hydrogen was not clear in his periodic table.

Q10. How were the drawbacks of Mendeleev's periodic table resolved in the modern periodic table?

Ans.  As the modern periodic table was based on the atomic numbers so all the isotopes could be placed together in one slot.  Secondly, the wrong order of atomic masses was also sorted as Cobalt's atomic number was lower than Nickel even though it had a higher atomic mass.

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