Why do we feel light on our feet when standing in a swimming pool with water up to our armpits?

A mug full of water appears light as long as it is under water in the bucket than when it is outside water. Why?

What happens to the buoyant force as more and more volume of a solid object is immersed in a liquid?

Explain why, big boulders can be moved easily by flood.

An iron nail sinks in water but it floats in mercury. Why?