if the pressure of n2/h2 in aclosed apparatus is 100 atm and 20 percent of the mixture then react ,the pressure at the same temperature would be

Answer 1

Is the initial mixture of N2 and H2 stoichiometric (1:3) ratio? That would make a difference in the answer.

There are other possible N-H compounds besides NH3.

This does not appear to be a well posed problem, but I am not a chemistry expert.