Which of the following solutions has maximum vapour pressure?

According to Raoult's law, the relative lowering of vapour pressure is directly proportional to the concentration of the solute particles in the solution.

$\dfrac{P^0 - P_s}{P^0} \propto C$

This implies that the vapour pressure of the solution ($P_s$) is inversely proportional to the concentration of the solute.

Among the given options, the $0.01$ M copper sulphate solution has the minimum concentration. Therefore, it will have the minimum lowering of vapour pressure and consequently the maximum vapour pressure.

Answer: 0.01 M copper sulphate solution