Question

how is raoult's law a special condition of Henry`s law

Answer 1

it is a spl case of henry law as in both of em P is directly proportional to mole fraction of gas ,the difference lies in the constants.
For Henry's law its Henry's constant Kh
whereas for Raoult's law it is P^a i.e. the pure pressure of gas A.

Answer 2

If we compare the equations for Raoult's law and Henry's law, it can be seen that the partial pressure of the volatile component or gas is directly proportional to its mole fraction  in solution. Only the proportionality constant KH differs from p01.  Thus, Raoult's law is  a special case of Henry's law where Henry's law constant becomes equal to vapour pressure of pure component.