Question

the dead body floats in the water while a man alive will sink

Answer 1

Things float in water if they are less dense than water, i.e. they weigh less than the same volume of water. The density of a human body with a lung full of air is about 0.985kg/l - slightly less than water (1.0kg/l) - which is why, if I throw you in a swimming pool, you'll float with a small amount of you (0.015 by weight out of the water). If you don't hold your breath because you panic or because you're dead, your weight remains the same, but your volume is smaller. Your density therefore increases to - about 1.08kg/l. This is higher than water so a dead body will actually sink.

Answer 2

the dead body floats in the water while a man alive will sink.

Dead body floats on water surface while a living body sink into water due to depend on density.

The dead man density lower than water.but the living body having density more than water.

This is the reason why dead body floats in water and living body sink in water.