What is the physical significance of hfg? can it be obtained from a knowledge of hf and hg? how?

Hfg is the amount of energy required to vaporize a given amount of saturated liquid. A saturated liquid is one which is about to vaporize, so it has both liquid and gaseous components, which have enthalpies hf and hg respectively.

Hfg may be determined from hf and hg using:

Hfg = hg - hf