Which of the following mixtures is called an acidic buffer?

An acidic buffer solution is prepared by mixing a proportionate quantity of

$A$ physician wishes to prepare a buffer solution at $pH = 3.58$ that efficiently resists changes in $pH$ yet contains only small concentration of the buffering agents. Which of the following weak acids together with its sodium salt would be best to use?

$A$ buffer solution contains $0.1 \ M$ of acetic acid and $0.1 \ M$ of sodium acetate. What will be its $pH$,if $pK_a$ of acetic acid is $4.75$?

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 statement is correct for a mixture of $1 \ M \ NaCl$ and $1 \ M \ HCl$?