Given, the two bodies should be in equilibrium even after these are dipped is liquids of different densities,
that means they have displaced the equal weights of liquids.
Weight of the oil displaced by larger block =2V×0.9×g .........(I)
Weight of the unknown liquid displaced by smaller block =V×ρ×g .........(II)
From eq 1 and 2 we get,
ρ=1.8 gm/cm3