19. In which of the following reactions, the equilibrium remains unaffected on addition of small amount of argon at constant volume?

(1) H2(g)+I2(g)2HI(g)

(2) PCl5(g)PCl3(g)+Cl2(g)

(3) N2(g)+3H2(g)2NH3(g)

(4) The equilibrium will remain unaffected in all the three cases

HINT-inert gas doesn't effect equilibrium at constant volume.
 
EXPLAINATION(4)
In these reactions, at constant volume
H2(g)+I2(g)2HI(g)
PCl5(g)PCl3(g)+Cl2(g)
N2(g)+3H2(g)2NH3(g)
The equilibrium constant (K) remains unaffected on addition of inert gas in all the three cases.