Sodium acetate $\left( CH _{3} COONa \right)=0.10\, M$;
Acetic acid $\left( CH _{3} COOH \right)=0.01\, M$;
$pH$ of acidic buffer solution is given by
$pH = pK _{ a }+\log \frac{[\text { Salt }]}{[\text { Acid }]}$
$=4.57+\log \left(\frac{0.1}{0.01}\right)$
$=5.57$
$A = NH_4Cl$; $ B = CH_3COONa$; $ C = NH_4OH$; $D = CH_3COOH$