Which among the following pairs is not an acidic buffer?

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

$pH$ of a mixture which is $0.1 \ M$ in $CH_3COOH$ and $0.05 \ M$ in $(CH_3COO)_2Ba$ is [$pK_a$ of $CH_3COOH$ = $4.74$]

Observe the following four solutions :
$P : 10 \ mL, 0.1 \ M \ NaOH + 5 \ mL, 0.1 \ M \ HCl$
$Q : 10 \ mL, 0.1 \ M \ NaOH + 15 \ mL, 0.1 \ M \ CH_3COOH$
$R : 10 \ mL, 0.1 \ M \ NH_3 + 10 \ mL, 0.1 \ M \ NH_4Cl$
$S : 10 \ mL, 0.05 \ M \ NaF + 5 \ mL, 0.1 \ M \ HF$
Which of above solutions act as buffer?

Which buffer solution out of the following will have $pH > 7$?

$0.1 \, M$ acetic acid solution is titrated against $0.1 \, M \, NaOH$ solution. What would be the difference in $pH$ between $1/4$ and $3/4$ stages of neutralization of acid?