When an acid or alkali is mixed with a buffer solution,the $pH$ of the buffer solution:

Which of the following is a buffer solution?

$100 \ mL$ of $0.1 \ M$ $HA$ (weak acid) and $100 \ mL$ of $0.2 \ M$ $NaA$ are mixed. What is the $pH$ of the resultant solution? ($K_{a}$ of $HA$ is $10^{-5}$; $\log 2 = 0.3$)

The $OH^{-}$ concentration in a mixture of $5.0 \ mL$ of $0.0504 \ M \ NH_{4}Cl$ and $2 \ mL$ of $0.0210 \ M \ NH_{3}$ solution is $x \times 10^{-6} \ M$. The value of $x$ is ..... .
(Nearest integer)
$[ \text{Given } K_{w}=1 \times 10^{-14} \text{ and } K_{b}=1.8 \times 10^{-5} ]$

Addition of sodium hydroxide solution to a weak acid $(HA)$ results in a buffer of $pH \ 6$. If ionisation constant of $HA$ is $10^{-5}$,the ratio of salt to acid concentration in the buffer solution will be

An acidic buffer is obtained on mixing