$50\mathrm{mL}$ of $0.10\mathrm{M}$ $\mathrm{HCl}$ is mixed with $50\mathrm{mL}$ of $0.10\mathrm{M}$ $\mathrm{CH}{}_3\mathrm{COOH}$ ($K_a=1.8\times 10^{-5}$) and titrated with $0.10\mathrm{M}$ $\mathrm{NaOH}$. Neglect the ionisation of water; where only the weak acid is present use the exact quadratic. Select the correct statement(s).

1. AAfter $25\mathrm{mL}$ of $\mathrm{NaOH}$ the pH is 1.70
2. BAfter $50\mathrm{mL}$ of $\mathrm{NaOH}$ the pH is about 3.1
3. CAfter $75\mathrm{mL}$ of $\mathrm{NaOH}$ the pH equals 5.24
4. DAfter $100\mathrm{mL}$ of $\mathrm{NaOH}$ the pH is 8.57