Solution

According to the infamous archimedes principle water applies an upthrust to the body submerged in it which in turn reduces the weight of the body. . It is easier to lift a heavy stone under water than in air because in water it experiences an upward buoyant force which balances the actual weight of the stone acting downwards. Thus, due to upthrust there is an apparent loss in the weight of the heavy stone which makes it lighter in water and hence easy to lift.