Question

why does vaseline applied leaf floats on water​

Answer 1

Cause the vasline layer covers the stomata which makes the density of the leaf thicker and thus the leaf floats

Answer 2

Answer:

Covering the lower side of the leaves with petroleum jelly (Vaseline) would block the stomata and prevent the evaporation of water from the leaf (Transpiration) and we know that transpiration is very important for the ascent of sap in plants. Hence, vaseline prevents ascent of sap.