Assertion (A) The ionisation of hydrogen sulphide in water is low in the presence of hydrochloric acid.
Reason (R) Hydrogen sulphide is a weak acid.
Assertion (A) For any chemical reaction at a particular temperature, the equilibrium constant is fixed and is a characteristic property.
Reason (R) Equilibrium constant is independent of temperature.
Assertion (A) Aqueous solution of ammonium carbonate is basic.
Reason (R) Acidic/basic nature of a salt solution of a salt of weak acid and weak base depends on $\mathrm{K}_{\mathrm{a}}$ and $\mathrm{K}_{\mathrm{b}}$ value of the acid and the base forming it.
Assertion (A) An aqueous solution of ammonium acetate can act as a buffer.
Reason (R) Acetic acid is a weak acid and $\mathrm{NH}_4 \mathrm{OH}$ is a weak base.
Assertion (A) In the dissociation of $\mathrm{PCl}_5$ at constant pressure and temperature the addition of helium at equilibrium increases the dissociation of $\mathrm{PCl}_5$.
Reason (R) Helium removes $\mathrm{Cl}_2$ from the field of action.