Assign $A, B, C, D$ for the given type of reaction:
$Mg(OH)_2 \downarrow + 2HCl \longrightarrow MgCl_2 + 2H_2O$

In which of the following equations will $\alpha_1$ or $\alpha_2$ be higher?
$(i) \, NH_4OH + H_2O \rightarrow \alpha_1$
$(ii) \, NH_4OH + D_2O \rightarrow \alpha_2$

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 $CH_3COOH$?

The $pH$ of the solution containing $10 \ mL$ of $0.1 \ N$ $NaOH$ and $10 \ mL$ of $0.05 \ N$ $H_2SO_4$ would be

Statement $A$: Addition of $NH_4OH$ in the presence of excess $NH_4Cl$ to an aqueous solution of $BaCl_2$ results in the precipitation of $Ba(OH)_2$.
Reason $B$: $Ba(OH)_2$ is insoluble in water.

Which of the following pairs of substances cannot exist together in a solution?