hello mr sujit,
2 * (h/g)^1/2...is the right answer.
Bcozz...i m not tellimg "the time taken by the stone to reach the maximum hight is 2 * (h/g)^1/2...it is the total time i.e. taken by the stone to reach the max hight where the velocity is zero & then come to the ground via height h."...okii
by the way if u can proove ur answer then it is better.
Becoz I m also not 100% sure....please calculate and wright how it is as u written the answer.......