A person runs for $1\text{ hour}$, $1\text{ hour}$, $1.5\text{ hours}$ and $1.5\text{ hours}$, respectively, along the sides of a square track. If length of each side is $20\text{ km}$, then his average speed in $\text{km/hour}$ is

A square track has 4 sides. Since the length of each side is $20\text{ km}$, the total distance covered around the track is:
$$\text{Total Distance}=4\times 20\text{ km}=80\text{ km}$$

The total time taken to complete the run is the sum of individual durations:

$$\text{Total Time}=1+1+1.5+1.5=5\text{ hours}$$

The average speed is defined as the total distance divided by the total time:

$$\text{Average Speed}=\frac{\text{Total Distance}}{\text{Total Time}}=\frac{80\text{ km}}{5\text{ hours}}=16\text{ km/hour}$$