Which of the following aqueous solutions, when added to 50 cm3 of 0.10 mol dm-3 propanoic acid (CH3CH2COOH\text{CH}_3\text{CH}_2\text{COOH}CH3CH2COOH), produces a buffer solution?
50 cm350\text{ cm}^350 cm3 of 0.10 mol dm−3 NaOH(aq)0.10\text{ mol dm}^{-3}\ \text{NaOH(aq)}0.10 mol dm−3 NaOH(aq)
25 cm325\text{ cm}^325 cm3 of 0.10 mol dm−3 HCl(aq)0.10\text{ mol dm}^{-3}\ \text{HCl(aq)}0.10 mol dm−3 HCl(aq)
25 cm325\text{ cm}^325 cm3 of 0.10 mol dm−3 NaOH(aq)0.10\text{ mol dm}^{-3}\ \text{NaOH(aq)}0.10 mol dm−3 NaOH(aq)
50 cm350\text{ cm}^350 cm3 of 0.10 mol dm−3 NaCl(aq)0.10\text{ mol dm}^{-3}\ \text{NaCl(aq)}0.10 mol dm−3 NaCl(aq)
