Here we are neglecting the buoyant force due to air and only buoyant force due to water is considered. Weight of stone in air, W = 250 N (W = mg); m is the mass and g is acceleration due to gravity Weight of stone in water, Ww=150N Total Force on stone, when it is submerged in water fully, F=mg−γw×Vsub Since stone is fully submerged so its submerged volume is the volume of stone i.e. Vsub=V Now, F=Ww=150N (Given) Mg=Ww=250N (Given) Putting these values, we get 150=250−10000×V ∴V=0.01m3