Which is the most efficient method for separating `D_2` from `H_2` ?

Write a method for the preparation of H_2O_2

Give the industrial method of preparation of H_2O_2

Hydrogen is the most abundant element in the universe. But in free state it is almost not found in earth's atmosphere. Suggest any three method for the preparation of H_2 , gas.

Hydrogen is the most abundant element in the universe, but in free state it is almost not found in earth's atmosphere. suggest any three methods for the preparation of H_2 gas by selecting suitable substance given below.