When $\mathrm{HF}$ is dissolved in formic acid, the equilibrium established is:-

$\mathrm{HF}+\mathrm{HCOOH}\rightleftharpoons {\mathrm{F}}^{-}+{\mathrm{HCOOH}}_2^{+}$

the true pair of conjugate acid base is as a [acid, conjugate acid] [Base, conjugate base]:-

$\mathrm{Assertion}:$ When small amount of acid or base is added to pure water, its $\mathrm{pH}$ undergoes a change.

$\mathrm{Reason}:$ Addition of an acid or base increases the degree of ionisation of water.

$\mathrm{Assertion}:$Solubility of $\mathrm{AgBr}$ decreases in the presence of sodium bromide.

$\mathrm{Reason}:$Sodium bromide undergoes hydrolysis in water.