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

Q. 4. Which of the following two metals will melt at body temperature (37° C)?
Gallium, Magnesium, Caesium, Aluminium.

Ans. Gallium and Caesium will melt at 37°C.

Q. 5. Light enters from air into glass having refractive index 1.50. The speed of light in vacuum is 3.0 × 108 ms–1. What will its speed in glass be?

Sol.

Q.6. Identify the type of reaction in the following example :
2 H₂ (g) +O₂ (g) 2 H₂O (l)

Ans. It is a combination reaction because in this reaction two substances combine to form a single substance.

Q. 7. Give reason of the following :
(a) Aluminium oxide is considered an amphoteric oxide.
(b) Ionic compounds conduct electricity in molten state.

Ans. (a) Aluminium oxide is considered an amphoteric oxide because aluminium oxide shows basic as well as acidic behaviour and reacts with both acids as well as bases to form salts and water.

Al₂O₃ (s) + 6HCl (aq) → 2 AlCl₃ (aq) + 3H₂O (Salt)

Al₂O₃ (s) + 2NaOH (aq) → 2NaAlO₂ (aq) + H₂O (Salt)

(b) Ionic compounds conduct electricity in molten state because when ionic solids melt, their crystalline structure is broken down and ions become free to move and conduct electricity.

Ans. (i) Copper wire can be used for electrical transmission lines because it has a low resistivity and thus it is a good conductor of electricity.
(ii) Manganin can be used for electrical heating devices because it’s resistivity is about 25 times more than that of copper and thus produces a lot of heat on passing current.

Science 2008 Question Papers Class X
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