Question

Define: a mug full of water appears light as long as it is under water in the bucket than when it is outside water. Why

Answer 1

The reason is bouyant force when it's inside water this force acts on from below the object so it feels lighter but out of water there is no bouyant force and hence its heavier.

Answer 2

your answer
this is because of upthrust that acts upwards and makes body light this also happens when the body immersed is less dense than water then it feels more upthrust

hope helps