Answer
At $0.5 \hspace{2px} h$ the velocity is maximum.
Work Step by Step
The slope of the given graph is the rate of change of distance with respect to time.
Also, the rate of change of distance with respect to time is velocity.
Thus, the slope of the given graph is velocity.
Since, slope is maximum at time $0.5\hspace{2px} h$.
Velocity will also be maximum at time $0.5\hspace{2px} h$.