Consider the following endothermic reaction taking place in a closed vessel - HSC - SSCE Chemistry - Question 14 - 2016 - Paper 1

Decreasing the volume of the closed vessel would shift the equilibrium position to the side with fewer moles of gas. In this case, the reactant side $N_2O_4(g)$ has fewer moles compared to the product side $2NO_2(g)$. Consequently, producing more $N_2O_4$ aligns with Le Chatelier's principle, leading to an increase in its concentration.