Which one is a mixed salt?

At $25 \, ^oC$,the concentration of $H^{+}$ and $OH^{-}$ ions in pure water is $1 \times 10^{-7} \, M$ each. Which of the following is equal to $2 \times 10^{-7} \, M$?

The dissociation constants for acetic acid and $HCN$ at $25\,^{\circ}C$ are $1.5 \times 10^{-5}$ and $4.5 \times 10^{-10}$ respectively. The equilibrium constant for the equilibrium $CN^{-} + CH_3COOH \rightleftharpoons HCN + CH_3COO^{-}$ would be

If $20 \, mL$ of $0.25 \, N$ strong acid and $30 \, mL$ of $0.2 \, N$ strong base are mixed,then the resulting solution is

What is the degree of dissociation of $CH_3COOH$ if $\wedge^{\circ}(CH_3COO^{-}) = 50 \ S \ cm^2 \ mol^{-1}$,$\wedge^{\circ}(H^{+}) = 350 \ S \ cm^2 \ mol^{-1}$ and the molar conductivity of $5 \times 10^{-2} \ M \ CH_3COOH$ is $20 \ S \ cm^2 \ mol^{-1}$?

If molar conductance at infinite dilution for $CH_3COO^-$ and $H^+$ ions are $50 \text{ S cm}^2 \text{mol}^{-1}$ and $350 \text{ S cm}^2 \text{mol}^{-1}$ respectively, and the molar conductivity of $5 \times 10^{-2} \text{ M}$ $CH_3COOH$ is $20 \text{ S cm}^2 \text{mol}^{-1}$, what is the hydrogen ion concentration in $\text{mol/dm}^3$ of $CH_3COOH$?