CBSE : Central Board Secondary Examination Science Paper 2008

CBSE : Central Board Secondary Examination Science Paper 2008

Class 10

Section A

1. Balance the following chemical equation :         1

Fe (s) + H20 (g) -> Fe304 (s) + H2 (g)

2. Why is respiration considered an exothermic process ?   1

3. How does the flow of acid rain water into a river make the survival of aquatic life in the river difficult ?       1

4. Draw the following diagram in your answer-book and show the formation of image of the object AB with the help of suitable rays.  1

Screenshot from 2014-02-15 14:57:11

5. Why is a series arrangement not used for connecting domestic electrical appliances in a circuit ?   1

6. Out of 60 W and 40 W lamps, which one has a higher electrical resistance when in use ?

7. Write the chemical formula for washing soda. How may it be obtained from baking soda ? Name an industrial use of washing soda other than washing clothes.

8. Give an example of a decomposition reaction. Dscribe an activity to illustrate such a reaction by heating.

9. Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed :

(a) at 2F1.
(b) between F1 and the optical centre O of lens.

10. What is meant by the term, ‘magnetic field’ ? Why does a compass needle show deflection when brought near a bar magnet ?

11. (a) Why are covalent compounds generally poor conductors of electricity ?

(b) Name the following compound :

Screenshot from 2014-02-15 14:57:28

(c) Name the gas evolved when ethanoic acid is added to sodium carbonate. How would you prove the presence of this gas ?

12. (a) What are amphoteric oxides ? Choose the amphoteric oxides from amongst the following oxides :

Na20, ZnO, A1203, C02, H20

(b) Why is it that non-metals do not displace hydrogen from dilute acids ?

13. Two lamps, one rated 60 W at 220 V and the other 40 W at 220 V, are connected in parallel to the electric supply at 220 V.

(a) Draw a circuit diagram to show the connections.
(b) Calculate the current drawn from the electric supply.
(c) Calculate the total energy consumed by the two lamps together when they operate for one hour

14. (a) Distinguish between the term ‘overloading’ and ‘short-circuiting’ as used in domestic circuit.

(b) Why are the coils of electric toasters made of an alloy rather than pure metal ?

15. On the basis of Mendeleev’s Periodic Table given below, answer the questions that follow the table :

 Group

I

II

III

IV

V

VI

VII

VIII

Oxide Hydride

R2O

rh

RO

RH2

R2°3

rh3

ro2 rh4

R2°5

rh3

ro3 rh2

r2o7

rii

ro4

Periods

A B

A B

A B

A B

A B

A B

A B

Transition series

1

H

1-008

2

Li

6-939

Be

9-012

B 10-81

c

12-011

N

14-007

0

15-999

F

18-998

3

Na 22-99

Mg 24-31

A1

29-98

Si

28-09

P

30-974

S

32-06

CI

35-453

4 First series :

Second series :

K

39-102

Cu 63-54

Ca

40-08

Zn 65-37

Sc 44-96

Ga 69-72

Ti 47-90

Ge 72-59

V

50-94

As

74-92

Cr 50-20

Se

78-96

Mn 54-94

Br

79-909

Fe Co Ni 55-85 58-93 58-71

5 First series :

Second series :

rb

85-47

Ag 107-87

Sr

87-62

Cd 112-40

Y

88-91

In

114-82

Zr 91-22

Sn

118-69

Nb 92-91

Sb

121-75

Mo 95-94

Te

127-60

Tc 99

i

126-90

Ru Rh Pd 101-07 102-91 106-4

6 First series :

Second series :

Cs

132-90

Au 196-97

Ba

137-34 Hg 200-59

La 138-91

Tl

204-37

Hf 178-49

Pb

207-19

Ta 180-95

Bi

208-98

W 183-85

Os Ir Pt 190-2 192-2 195-09

(a) Name the element which is in

(i)Ist group and 3rd period.

(ii)VIIth group and 2nd period.

(b)Suggest the formula for the following :

(i) oxide of nitrogen

(ii) hydride of oxygen

(c) In group VIII of the Periodic Table, why does cobalt with atomic mass 58-93 appear before nickel having atomic mass 58-71 ?

(d) Besides gallium, which two other elements have since been discovered for which Mendeleev had left gaps in his Periodic Table ?

(e) Using atomic masses of Li, Na and K, find the average atomic mass of Li and K and compare it with the atomic mass of Na. State the conclusion drawn from this activity. 5

OR

(a) Why do we classify elements ?

(b) What were the two criteria used by Mendeleev in creating his Periodic Table ?

(c) Why did Mendeleev leave some gaps in his Periodic Table ?

(d) In Mendeleev’s Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon ?

(e) Would you place the two isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same ? Justify your answer. 5

16. (a) What is meant by despersion of white light ? Describe the formation of rainbow in the sky with the help of diagram.

(b) What is hypermetropia ? Draw ray diagrams to show the image formation of an object by :

(i) Hypermetropic eye

(ii) Correction made with a suitable lens for hypermetropic eye

OR

(a) Give reasons for the following:

(i) Color of the clear sky is blue.

(ii) The sun can be seen about two minutes before actual sunrise.

(iii) We cannot see an object clearly if it is  placed very close to the eyes.

(b) What is Presbyopia ? Write two causes of this defect.

SECTION B

17. Which one of the following is a renewable resource ?
Natural gas, Petroleum. Ground water, Coal

18. What is the effect of DNA copying which is not perfectly accurate on the reproduction process ?

19. How do autotrophs obtain CG2 and N2 to make their food ?

20. List any four characteristics of bio gas an account of which it is considered an ideal fuel.

21. Discuss one limitation each for the extracting of energy from :

(a) winds

(b) tides

22. Write one function each of the following components of the transport system in human beings :
(a) Blood vessels
(b) Blood platelets
(c) Lymph
(d) Heart

23. Name one sexually transmitted disease each caused due to bacterial infection and viral infection. How can these be prevented ?

24. What are fossils ? What do they tell about the process of evolution ?

25. How is ozone formed in the upper atmosphere ? Why is damage to ozone layer a cause of concern to us ? What causes this damage ?

26. How are oxygen and carbon dioxide transported in human beings? How are lungs designed to maximize the area for exchange of gases?

27. (a) Draw the structure of a neuron and label the following on it :

Nucleus, Dendrite, Cell body and Axon

(b) Name the part of neuron:

(i) where information is acquired.

(ii) Through which information travels as an electrical impluse.

OR

(a) What is (i) phototropism and (ii) geotropism ? With labelled diagrams describe an activity to show that light and gravity change the direction that plant parts grow in.

(b) Mention the role of each of the following plant hormones :
(i) Auxin
(ii) Abscisic

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