The correct relation for speed is:

1. Speed = distance x time

2. Speed = $\dfrac{\text{distance}}{\text{time}}$

3. Speed = $\dfrac{\text{time}}{\text{distance}}$

4. Speed = $\dfrac{\text{1}}{\text{distance x time}}$

A boy travels a distance 150 m in 1 minute. His speed is:

1. 150 m s^-1
2. 2.5 m s^-1
3. 25 m s^-1
4. 9 m s^-1

State and define the S.I. unit of volume.

State two smaller units of volume. How are they related to the S.I. unit?