Which of the following will produce a buffer solution when mixed in equal volumes?
(i) 0.1 mol dm–3 NH4OH and 0.1 mol dm–3 HCl
(ii) 0.05 mol dm–3 NH4OH and 0.1 mol dm–3 HCl
(iii) 0.1 mol dm–3 NH4OH and 0.05 mol dm–3 HCl
(iv) 0.1 mol dm–3 CH4COONa and 0.1 mol dm–3 NaOH