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

(1) ${\mathrm{H}}_{2}\left(\mathrm{g}\right)+{\mathrm{I}}_{2}\left(\mathrm{g}\right)⇌2\mathrm{HI}\left(\mathrm{g}\right)$

(2) ${\mathrm{PCl}}_{5}\left(\mathrm{g}\right)⇌{\mathrm{PCl}}_{3}\left(\mathrm{g}\right)+{\mathrm{Cl}}_{2}\left(\mathrm{g}\right)$

(3) ${\mathrm{N}}_{2}\left(\mathrm{g}\right)+3{\mathrm{H}}_{2}\left(\mathrm{g}\right)⇌2{\mathrm{NH}}_{3}\left(\mathrm{g}\right)$

(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
${\mathrm{H}}_{2}\left(\mathrm{g}\right)+{\mathrm{I}}_{2}\left(\mathrm{g}\right)⇌2\mathrm{HI}\left(\mathrm{g}\right)$
${\mathrm{PCl}}_{5}\left(\mathrm{g}\right)⇌{\mathrm{PCl}}_{3}\left(\mathrm{g}\right)+{\mathrm{Cl}}_{2}\left(\mathrm{g}\right)$
${\mathrm{N}}_{2}\left(\mathrm{g}\right)+3{\mathrm{H}}_{2}\left(\mathrm{g}\right)⇌2{\mathrm{NH}}_{3}\left(\mathrm{g}\right)$
The equilibrium constant (K) remains unaffected on addition of inert gas in all the three cases.