Question

Give reason for the following a)when we warm a liquid,we should warm it from bellow

Answer 1

When we warm a liquid from its top then the water can't be heated properly...
And gets settled on its upper surface..
So we always warm the liquid from below..

Answer 2

any liquid on being warmed becomes less dense and thus tends to move upwards in the container. then the colder liquid moves down and again gets warmed up this repeating the same process.
if heated from the top.... the warm water remains at the top and the entire liquid does not get heated