Which of the following mixtures forms an acidic buffer?

Which of the following will not function as a buffer solution?

$A$ solution of $0.1 \ mol$ of $CH_3NH_2$ $(K_b = 5 \times 10^{-4})$ and $0.08 \ mol$ of $HCl$ is diluted to $1 \ L$. The $pOH$ of the resulting solution is $(\log 1.25 = 0.1)$.

What is the concentration of $[H^+]$ in $mol/L$ in a mixed solution of $0.20 \ M \ CH_3COONa$ and $0.10 \ M \ CH_3COOH$? (Given: $K_a$ of $CH_3COOH = 1.8 \times 10^{-5}$)

Explain the preparation of an acidic buffer solution with an example.

$50 \ mL$ of $0.02 \ M$ $NaOH$ solution is mixed with $50 \ mL$ of $0.06 \ M$ acetic acid solution. The $pH$ of the resulting solution is $......$ ($pK_a$ of acetic acid is $4.76$,$\log 2 = 0.30$).