Oxidation of ammonia is exothermic : ${\text{4NH}}_{\text{3}\left(\text{g}\right)}{\text{+\hspace{0.17em}5O}}_{\text{2}\left(\text{g}\right)}\rightleftharpoons {\text{\hspace{0.17em}4NO}}_{\left(\text{g}\right)}{\text{\hspace{0.17em}+\hspace{0.17em}6H}}_{\text{2}}{\text{O}}_{\left(\text{g}\right)}\text{\hspace{0.17em}+\hspace{0.17em}905.6kJ}$ equilibrium

system suggests that

On increasing temperature, equilibrium mixture will have less [NO] 

On increasing temperature, equilibrium constant remains unchanged

On increasing pressure, equilibrium mixture will have more $\left[{\text{NH}}_{\text{3}}\right]$

Addition of He at constant pressure promote the oxidation of ${\text{NH}}_3$