How many of the following may act as buffer ?
(a) `20mL 0.2 M -H_(2)CO_(3)` solution `+10 ml 0.2 M-NaOH` solution
(b) `20 ml 0.2 M -H_(2)CO_(3)` solution `+20 ml 0.2 M-NaOH` solution
(c) `20 mL 0.2 M-H_(2)CO_(3)` solution `+30 mL 0.2 M-NaOH` solution
(d) `20 mL 0.2 M - H_(2)CO_(3)` solution `+10 mL 0.2 M-NaHCO_(3)` solution
(e) `20 mL 0.2 M -H_(2)CO_(3)` solution `+10 mL 0.2 M-Na_(2)CO_(3)` solution
(f) `20 mL 0.2 M -H_(2)CO_(3)` solution `+20 mL 0.2 M -Na_(2)CO_(3)` solution
(g) `20 mL 0.2 M -H_(2)CO_(3)` solution `+30 ml 0.2 M-Na_(2)CO_(3)` solution

Answer

5