Inert gas (He) is added to gaseous equilibria. Select the correct statements.

AAt constant $T$ and $V$ , addition of He does not shift any gaseous equilibrium
BAt constant $T$ and $P$ , addition of He does not shift $H X_{2} + Cl X_{2} 2 HCl$
CAt constant $T$ and $P$ , addition of He to $N X_{2} + 3 H X_{2} 2 NH X_{3}$ shifts it forward
DAt constant $T$ and $P$ , addition of He to $N X_{2} O X_{4} 2 NO X_{2}$ increases the amount of $NO X_{2}$

Answer: A, B, D

At constant volume, partial pressures of reacting gases do not change, so no shift (A). At constant

P

, He expands the volume, which favours the side with more gas moles: no shift for

Δ n = 0

(B), backward for

N X_{2} + 3 H X_{2} 2 NH X_{3}

(

Δ n = - 2

, so C is false), forward for

N X_{2} O X_{4} 2 NO X_{2}

(D).