Which of the following mixtures forms an acidic buffer?

For preparing a buffer solution of $pH = 5$ by mixing sodium acetate and acetic acid,the ratio of the concentration of salt and acid should be $(K_a = 10^{-5})$:-

An acidic buffer is obtained on mixing

The Henderson-Hasselbalch equation for an acidic buffer is given by $pH - pK_a = 5$. This condition holds true when:

In a mixture of a weak acid and its salt,the ratio of concentration of acid to salt is increased ten-fold. The $pH$ of the solution

If $20 \ mL$ of $0.1 \ M \ NaOH$ is added to $30 \ mL$ of $0.2 \ M \ CH_3COOH$ $(pK_a = 4.74)$,find the $pH$ of the resulting solution.