Which of the following relations is correct?
$(i).\ Speed=Distance\times Time$
$(ii).\ Speed=\frac{Distance}{Time}$
$(iii).\ Speed=\frac{Time}{Distance}$
$(iv).\ Speed =\frac{1}{Distance\times Time}$

The correct answer is: $(ii).\ Speed=\frac{Distance}{Time}$

Explanation:

Distance traveled per unit of time by a moving object is called its speed. 

So, $\boxed{Speed=\frac{Distance}{Time}}$

The above relation can also be expressed in the following ways:

$\boxed{Time=\frac{Distance}{speed}}$

$\boxed{Distance=Speed\times Time}$

SI unit of speed is meter per second$(m/s)$.

Therefore, only $\boxed{Speed=\frac{Distance}{Time}}$ is the correct relation among the given relations.

Hence, option $(ii).\ Speed=\frac{Distance}{Time}$ is correct.