Which of the following is a buffer solution?

What is the $pH$ of a buffer solution prepared by mixing $0.01 \ M$ weak acid and $0.02 \ M$ salt of weak acid with a strong base? $(pK_{a} = 4.680)$

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

$A$ weak acid of dissociation constant $10^{-5}$ is being titrated with aqueous $NaOH$ solution. The $pH$ at the point of one-third neutralization of the acid will be:-

The $pH$ of a buffer solution decreases by $0.02$ units when $0.12 \ g$ of acetic acid is added to $250 \ mL$ of a buffer solution of acetic acid and potassium acetate at $27^{\circ} C$. The buffer capacity of the solution is

The $pH$ of a buffer solution containing $25 \ mL$ of $1 \ M \ CH_3COONa$ and $25 \ mL$ of $1 \ M \ CH_3COOH$ will be appreciably affected by $5 \ mL$ of