Question

why does water roll off the surface of a leaf

Answer 1

as water does not have pufect shape and leaf has waxy coating on it

Answer 2

The water roll off the surface of a leaf as it has a layer of wax on the surface of the leaves.

The wax-coated surface cannot absorb water.

As a result the leaves of plant cannot absorb the water through the leaves.

The water rolls off instead of getting absorbed.