Which of the following mixtures will form a buffer solution?

What is the $pH$ of $10 \ L$ of a buffer solution containing $0.01 \ M \ NH_4Cl$ and $0.1 \ M \ NH_4OH$ having $pK_b$ of $5$?

Find $pH$ of the resultant solution formed by the addition of $500 \ mL$ $0.1 \ M$ $Ba(OH)_2$ and $500 \ mL$ $0.6 \ M$ $NH_4Cl$ in $1 \ L$ pure $H_2O$ at $25 \ ^oC$ (Use $\log \ 2 = 0.3$,$\log \ 3 = 0.5$,$\log \ 5 = 0.7$,$K_b(NH_3) = 10^{-5}$)

Which of the following buffers is used to maintain the $pH$ of human blood naturally?

Calculate the $pH$ of a buffer solution containing $6.1 \times 10^{-2} \ M$ sodium acetate $(CH_3COONa)$ in $1 \ L$ of $0.1 \ M$ acetic acid $(CH_3COOH)$ solution. (Given: $pK_a$ of $CH_3COOH = 4.76$)

If $50 \, mL$ of $2 \, N$ acetic acid is mixed with $10 \, mL$ of $1 \, N$ sodium acetate solution,what will be the approximate $pH$ of the resulting solution? (Given: $K_a = 10^{-5}$)