Answer
$\text { (d) } \mathrm{N}_2 \rightarrow 2 \mathrm{~N}
$
Work Step by Step
When an inert gas is added at constant pressure and temperature, the volume increases.
This effectively reduces the partial pressures (concentrations) of all reacting gases.
Equilibrium will shift toward the side with more moles of gas, to counter the reduction.
The reaction $\text { (d) } \mathrm{N}_2 \rightarrow 2 \mathrm{~N}$ is the one where the number of moles of products increases upon adding inert gases at constant pressure and temperature, because the equilibrium shifts toward the side with more gas molecules.
The corect answer is (d).
