Amongst the following solutions,the buffer solution is

$50 \ mL$ 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 $4.76$,$\log 2 = 0.30$).

Which of the following is a buffer solution?

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

$40 \ mL$ of $0.1 \ M$ ammonia solution is mixed with $20 \ mL$ of $0.1 \ M \ HCl$. What is the $pH$ of the mixture? ($pK_b$ of ammonia solution is $4.74$).

$0.1 \ mol$ of $CH_3NH_2$ $(K_b = 5 \times 10^{-4})$ is mixed with $0.08 \ mol$ of $HCl$ and diluted to $1 \ L$. The $[H^{+}]$ in the solution is: