Which of the following will produce a buffer solution when mixed in equal volumes?
1
0.1 mol dm–3 NH4OH and 0.1 mol dm–3HCl
2
0.05 mol dm–3 NH4OH and 0.1 mol dm–3 HCl
3
0.1 mol dm–3 NH4OH and 0.05 mol dm–3 HCl
4
0.1 mol dm–3 CH4COONa and 0.1 mol dm–3 NaOH