A body of 200g begins to fall from a height where its potential energy is 80 J. Its velocity at a point where kinetic and potential energies are equal is

Maa of the body is 200 g, or 0.2 kg.
The total energy of the system is determined by the conservation of energy, which states that the sum of the system's potential and kinetic energy is constant at all times.

$$\begin{gathered} \mathrm{KE}+\mathrm{PE}=80\mathrm{J} \\ \Rightarrow \mathrm{KE}=40\mathrm{J} \end{gathered}$$

When a body's kinetic energy and potential energy are equal, let's say its velocity is v.

$$\begin{gathered} \frac{1}{2}{\mathrm{mv}}^2=40 \\ \Rightarrow \frac{1}{2}\times 0.2\times {\mathrm{v}}^2=40 \\ \Rightarrow {\mathrm{v}}^2=400 \\ \Rightarrow \mathrm{v}=20\mathrm{m}/\mathrm{s} \end{gathered}$$

Hence the correct answer is 20m/s.