What is the $pH$ of a buffer solution prepared by mixing $0.01 \ M$ weak acid and $0.02 \ M$ salt of weak acid with a strong base? $(pK_{a} = 4.680)$

$A$ buffer solution can be prepared by mixing which of the following?

Which of the following solutions does not act as a buffer $:-$

Calculate the $pH$ of a $2 \, L$ solution containing $0.1 \, M \, CH_3COOH$ and $0.1 \, M \, (CH_3COO)_2Ba$. Given $K_a (CH_3COOH) = 1.8 \times 10^{-5}$.

For a weak acid $(HA)$,$pK_a = 4.5$. The $pOH$ of a buffer solution of $HA$ in which $50\%$ of the acid is ionized is:

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