A $0.10\mathrm{M}$ solution of ammonium formate, $\mathrm{HCOONH}{}_4$, is prepared. Take $K_a(\mathrm{HCOOH})=1.8\times 10^{-4}$ ($\mathrm{p}{K}_a=3.75$), $K_b(\mathrm{NH}{}_3)=1.8\times 10^{-5}$ ($\mathrm{p}{K}_b=4.75$) and $K_w=1.0\times 10^{-14}$. Use $\mathrm{pH}=7+\frac{1}{2}(\mathrm{p}{K}_a-\mathrm{p}{K}_b)$ and $h=\sqrt{K_w/(K_a{K}_b)}$. Select the correct statement(s).

1. AThe pH of the solution is 6.50
2. BThe pH changes appreciably if the solution is diluted to $0.010\mathrm{M}$
3. CThe degree of hydrolysis of the salt is about $1.8\times 10^{-3}$
4. D$[\mathrm{NH}{}_3]$ and $[\mathrm{HCOOH}]$ are nearly equal, each about $1.8\times 10^{-4}\mathrm{M}$