A mixture of Nitrogen and Hydrogen is at an initial pressure of 200atm. If 20% of the mixture reacts by the time equilibrium is reached, the equilibrium pressure of the mixture is

Initial pressure of mixture containing Nitrogen & Hydrogen = 200 atm;

Percentage of the mixture reacted = 20%

Thus decrease in pressure due to reaction

Pressure $\propto$ number of moles

4 moles of reactants give 2 moles of products.

Thus if the decrease in pressure of reactant is 40 atm then increase in pressure of product

Initial moles	200 atm		-
Pressure at equilibrium	(200 - 40) atm		20 atm

$\therefore$Equilibrium pressure = (160 + 20) atm

                                      = 180 atm