if the water molecules in 1g of water were uniformly distributed on earth surface , how many such water molecules would there be in 1 cm^2 of earth?

No. of molecules in 1g of water : (1/18)*6.023x10^23 = 3.34 * 10^22.

Area of earth ( consider it a sphere ) = 4x3.14x6400*10^5 cm

Therefore your answer = 6.023x10^23/(8.03x10^9)

                                = 7.5x10^13

i dont get the solution and also answer is not right.

Wellthis is the answer and the way is vey clear too.