Statement (A): Inside a charged hollow metal sphere, $E = 0, V\ne 0.$ (E-electric field, V-electric potential) 

Statement (B): The work done in moving a positive charge on a equipotential surface is zero. 

Statement (C): When two like charges are brought closer, their mutual electrostatic potential energy will increase.

Inside a hollow metal sphere $\mathrm{E}=0 \text{and }\mathrm{V}=\frac{KQ}{R}\ne 0$

So, (A) is true,

No work is done in moving a charge from one point to other on equipotential
surface as $\mathrm{\Delta }V=0$ on equipotential
surface. So $W = q$
$\mathrm{\Delta }V=0$. 

So, (B) is true.

When two like charges are brought closer, then external agent do the work against the mutual repulsion. So potential energy of system increases. 

So, (C) is true.