A vessel is partly filled with a liquid. coefficients of cubical expansion of material of the vessel and liquid are γV and γL, respectively. If the system is heated, then volume unoccupied by the liquid will necessarily

Since the vessel is partly filled, volume of the vessel is greater than that of the liquid. When a body having volume V is heated through ∆θ,then increase in its volume is given by     ΔV=V⋅γ⋅ΔθSince, γV=γL, therefore ΔV∝V. Hence, on heating expansion of vessel will be greater than that of liquid. It means unoccupied volume will necessarily increase. So, option (b) is correct.