If the amount of n2 is decreased in the reaction,

The reaction will proceed to wards left to regain the equilibrium.

Explanation:

Equilibrium:

This is the state of reaction in which the rate of forward reaction and reverse reaction are same.

There are three factors that effect the equilibrium condition.

The change in concentration

The change in volume

The change in temperature

In given equilibrium reaction,

3H₂ + N₂  ⇄  2NH₃

when amount of N₂ is decreased it means more amount of product is on right side and equilibrium is disturb. Thus equilibrium is shifted toward the left produces more N₂  and regain the equilibrium.

the correct answer is:

a. formation of precipitation