Science 2011 CBSE [ Delhi ] Set III
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Q1
What makes the earth’s atmosphere a heterogeneous mixture?
Marks:1View AnswerAnswer:
Different composition of various gases makes the earth’s atmosphere a heterogeneous mixture that consists of 21% oxygen, 78% nitrogen, 0.93% argon and 0.03% CO2 with other gases.
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Q2
Write the electron dot structure of ethane molecule, C2H6.
Marks:1View AnswerAnswer:
The electron dot structure of ethane molecule, C2H6, is as follows:
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Q3
What are the various steps in a food chain called?
Marks:1View AnswerAnswer:
The various steps in a food chain are known as trophic levels.
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Q4
What is the important function of the presence of ozone in earth’s atmosphere?
Marks:1View AnswerAnswer:
The ozone layer acts as a shield and protects the earth from the harmful U.V. rays coming from the sun.
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Q5
List any four characteristics of a good fuel.
Marks:2View AnswerAnswer:
The four characteristic of good fuel are:
(i) It should produce high energy output per unit volume or mass.
(ii) It should have low ignition temperature.
(iii) It should be safe and easy to use.
(iv) It should leave no residue after burning. -
Q6
What are non-renewable resources of energy? Give two examples of such resources.
Marks:2View AnswerAnswer:
Non-Renewable sources of energy are those which are exhaustible, and cannot be replaced once they have been used.
Coal and petroleum are two main examples of non-renewable sources of energy. -
Q7
State two laws of reflection of light.
Marks:2View AnswerAnswer:
The two laws of reflection of light are as follows:
(i) The incident ray, the reflected ray and the normal at the point of incidence, all three lie in same plane.
(ii) The angle of reflection is always equal to angle of incidence. -
Q8
The stars appear higher from horizon than they actually are. Explain why is it so.
Marks:2View AnswerAnswer:
As we go down the atmosphere, the optical density increases. When the light from a star comes down, the dense air bends the light ray more and more towards the normal. When an observer interprets the image along the direction of final refracted rays, the position of star appears to be shifted above the actual position.
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Q9
Explain why the planets do not twinkle but the stars twinkle.
Marks:2View AnswerAnswer:
Due to point size appearance from the earth, position of the stars and the intensity of light coming from them both vary continuously due to the continuous change in the atmospheric density. The apparent position of the star fluctuates and the amount of starlight entering the eye flickers, this produces the twinkling effect.
Planets are considered in the form of disk. The darkest parts of the twinkle cycle from one part of the disk may be overlapped by focused light from other regions of the disk, keeping the light intensity closer to some mean value and reducing fluctuation. So, planets do not twinkle. -
Q10
(i) How do you calculate the possible valency of an element from the electronic configuration of its atoms?
(ii) Calculate the valency of element X whose atomic number is 9.Marks:2View AnswerAnswer:
(i) The electrons present in the last shell determine the valency of a particular element. If
(a)Number of valence electrons ≤4
Then, valency = number of valence electrons
(b)Number of valence electrons >4
Then, valency = 8 – number of valence electrons
Its valency = 8–7 =1 Hence, the valency of element with atomic number 9 is 1.
