CBSE Guess > Papers > Question Papers > Class X > 2008 >Science > Science Theory

(c) Electron dot structure of ethene (C₂H₄ ).

Section B

Q.17. List two main advantages associated with solar cells. 1

Ans. Advantages of solar cells :
(i) They have no moving parts, they require almost no maintenance.
(ii) They can be set up in remote, inaccessible areas where the laying of usual power transmission lines is difficult and expensive.

Q.19. What is the role of the acid in our stomach?

Ans. Role of acid in our stomach :
(i) It makes the medium acidic so that the enzyme pepsin can digest the proteins properly.
(ii) It kills any bacteria which may enter the stomach with food.

Q.20. How is energy generated in a nuclear fission reaction? Why is the large scale use of nuclear energy prohibitive?

Ans. (i) During fission the heavy nucleus of a radio-active atom (such as uranium, plutonium or thorium) splits up into smaller nuclei when bombarded with low energy neutrons with release of tremendous amount of energy. There is a small loss of mass in the nuclear fission process which is transformed into tremendous amount of energy.

(ii) The large scale use of nuclear energy is prohibitive because

• The waste products of nuclear reactions are radioactive which keep on emitting harmful nuclear radiations for thousands of years. So it is very difficult to store or dispose off nuclear wastes safely.
• There is the risk of accidents in nuclear reactors which may lead to the leakage of radioactive materials causing serious damage to living organisms.

Q.21. List any four changes you would like to incorporate in your life-style in a move towards a sustainable use of available resources in our country.

Ans. Four changes I would like to incorporate in my life-style as a move towards a sustainable use of available resources.
(i) I will reduce the use of petrol by walking or cycling for short distances.
(ii) I will reduce the wastage of electricity by switching off unnecessary electrical appliances.
(iii) I will send the discarded items of paper, plastic, glass and metal to the respective industries for making fresh paper, plastic, glass and metal objects.
(iv) I will ensure a continuous use of books by passing them on to my juniors.

Science 2008 Question Papers Class X
Delhi		Outside Delhi		Compartment Delhi		Compartment Outside Delhi
	All Sets (PDF)				Set 1		Set 1
					Set 2		Set 2
					Set 3		Set 3