WAEC Past Questions and Answers - Page 3075

15,371.

A vapour whose molecules are in dynamic equilibrium with those of its own liquid is said to be

A.

unsaturated

B.

gaseous

C.

saturated

D.

diffused

Correct answer is C

A saturated vapour is one which is in a dynamic equilibrium with its own liquid

15,372.

The maximum density of water occurs at a temperature of

A.

0°C

B.

4°C

C.

37°C

D.

273°C

Correct answer is B

This is as a result of the Hydrogen bonding in water. Due to the high Kinetic Energy of water, the hydrogen bonds can't hold for too long but from 4°C, there's an increase in the hydrogen bonds hence strenghtening it.  From the point of production of more hydrogen bonds, the bonding is no longer easily broken. Generally, these and a few factors based on these cause the density of water to be maximum at 4°C.

15,373.

Thermal energy added or removed from a substance that changes the state of the substance is called

A.

latent heat

B.

heat of reaction

C.

calorimetry

D.

specific heat

Correct answer is A

Latent heat is thermal energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process.

15,375.

Which of the following devices converts light energy to electrical energy?

A.

Bulb

B.

Television

C.

Solar cell

D.

Light emitting diode (LED)

Correct answer is C

The solar cell converts light from the sun to electricity.