For the reaction ${\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\rightleftharpoons 2{\mathrm{NH}}_3\left(\mathrm{g}\right)+93.6\mathrm{kJ}$ the concentration of ${\mathrm{NH}}_3$ at equilibrium will increase if

For the reaction ${\mathrm{N}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)\rightleftharpoons 2{\mathrm{NH}}_3\left(\mathrm{g}\right)+93.6\mathrm{kJ}$ the concentration of ${\mathrm{NH}}_3$ at equilibrium will increase if the temperature of the system is lowered

Le Chatelier's principle states that since the reaction is exothermic, increasing the temperature causes the equilibrium to move to the left and lowers the equilibrium concentration of ammonia. In other words, a high ammonia output benefits from low temperature and high pressure. No change in equilibrium will result with the addition of argon (Ar).

Hence option A is correct