Question

If we take a deep a breath and hold it for few seconds then our body seems to float more and when we breathe out our body floats less or submerges with the water explain why this happens

Answer 1

Humans evolved from sea creatures but—looking at our bodies—you'd never know it. We couldn't be less well suited to moving through water if we tried. We don't float too well, can't breathe for long beneath the surface, and rapidly tire as we thrash through the waves trying to move ourselves along; in a straight race with a dolphin or a shark, you'll always come last! But there's one big advantage we humans do have: we know about science. We understand how forces work and how to use them to our advantage. If you've never thought about swimming as a science, now's the time to start. Apply some scientific thinking and you'll find you can swim much more effectively. If you're a nervous nonswimmer, thinking about the solid science that keeps people afloat can give you enough confidence to break through your fear. So what are we waiting for? Let's take the plunge—with a closer look at the science of swimming!
Floating and buoyancy

Things float because when we place them in water, the pressure of the water underneath them pushes up and supports them; in other words, water pressure pushing upward balances weight (the force of gravity) pulling downward. That's one of the reasons why we swim in a horizontal position: spreading the body flat makes it work more like a raft, so there's more upthrust from the water below. You probably know that it's much easier to float on your back than standing straight upward, when you need to "tread water" (kick and push your arms downward to create an upward force that stops you sinking).