What is the total number of buffers formed during the titration of $H_3PO_4$ with $NaOH$?

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

What is $[H^{+}]$ in $mol/L$ of a solution that is $0.20\, M$ in $CH_3COONa$ and $0.10\, M$ in $CH_3COOH$? $K_a$ for $CH_3COOH = 1.8 \times 10^{-5}$.

$A$ buffer solution contains $0.1 \ mol$ of sodium acetate dissolved in $1000 \ cm^{3}$ of $0.1 \ M$ acetic acid. To the above buffer solution,$0.1 \ mol$ of sodium acetate is further added and dissolved. The $pH$ of the resulting buffer is

Buffer system helps to maintain blood $pH$ between .......

At a constant temperature,the $pK_b$ of $NH_4OH$ is $4.74$. What is the $pH$ of a basic buffer containing equimolar concentrations of $NH_4OH$ and $NH_4Cl$?