Give Reasons for the following: Why does a mug full of water feel lighter inside water?

Hint: With the help of Archimedes principle we can understand the given situation. Archimedes' principle states that at rest when a body is submerged in water or any fluid it will experience an upward force.

Complete answer:
Water is made up of small molecules which are attracted to each other with covalent bonds.According to Archimedes' principle when a body completely or partially is submerged in water a force is acted upon it in the upward direction. This force is known as buoyant force.When a body is submerged in water it displaces a volume of water equal to its own volume.

So, the buoyant force is equal to the weight of the water displaced by the submerged body.Hence, when a mug full of water is inside the water it displaces water equal to its volume. So buoyant force is acted on it which is upward in direction so the net force on the mug full of water inside water is equal to the force due to actual weight minus buoyant force acting on the body.

Therefore, the mug full of water feels lighter inside the water.

Note: Gravity is responsible for the buoyant force, but buoyant force acts in the upward direction. Because of the (gravitational) weight of the fluid above, fluid pressure rises with depth. This rising pressure exerts a force on a submerged item that grows in proportion to its depth.