Given $K_w=1.0\times 10^{-14}$; for $\mathrm{H}{}_2\mathrm{CO}{}_3$: $K_{a1}=4.3\times 10^{-7}$, $K_{a2}=4.7\times 10^{-11}$; for $\mathrm{H}{}_3\mathrm{PO}{}_4$: $K_{a1}=7.5\times 10^{-3}$, $K_{a2}=6.2\times 10^{-8}$. Select the correct statement(s) about aqueous solutions of amphiprotic salts.

1. A$\mathrm{NaHCO}{}_3$ solution is basic because $K_w/K_{a1}>K_{a2}$ for $\mathrm{H}{}_2\mathrm{CO}{}_3$
2. B$\mathrm{NaH}{}_2\mathrm{PO}{}_4$ solution is acidic because $K_{a2}>K_w/K_{a1}$ for $\mathrm{H}{}_3\mathrm{PO}{}_4$
3. C$\mathrm{NaH}{}_2\mathrm{PO}{}_4$ solution is basic because it is a sodium salt of a strong base
4. DDiluting a $\mathrm{NaHCO}{}_3$ solution ten times changes its pH by about one unit