Which of the following is not a buffer solution?

$A$ buffer solution is prepared with a concentration of $0.30 \ M \ NH_3$ and $0.20 \ M \ NH_4^+$. If the equilibrium constant for $NH_3$ is $K_b = 1.8 \times 10^{-5}$,what will be the $pH$ of this solution?

$A$ buffer solution contains $1 \ mol$ of ammonium sulphate and $1 \ mol$ of $NH_4OH$ $(K_b = 10^{-5})$. The $pH$ of the solution will be:

Assertion : Buffer system of carbonic acid and sodium bicarbonate is used for the precipitation of hydroxides of third group elements.
Reason : It maintains the $pH$ to a constant value,about $7.4.$

The dissociation constant of a weak acid is $1 \times 10^{-4}.$ In order to prepare a buffer solution with a $pH = 5,$ the $[Salt]/[Acid]$ ratio should be

An acidic buffer solution is prepared by mixing a proportionate quantity of