Which of the following is a buffer solution?

The $pH$ of blood is

The $pH$ of blood does not appreciably change by a small addition of acid or a base because blood

$0.1 \ mol$ 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:

What will be the change in $pH$ by adding $0.1 \ M \ NH_4Cl$ to $0.1 \ M \ NH_4OH$ (weak base) solution? (Given: $K_b$ of $NH_4OH = 1.77 \times 10^{-5}$)

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