The solutions of $\text{Mg(NO}_3)_2$ and $\text{Ba(NO}_3)_2$ are treated separately through a sequence of reactions. $\text{Mg(NO}_3)_2(aq) \xrightarrow{\text{sodium carbonate solution}} M \xrightarrow{\text{excess HCl}(aq)} N \xrightarrow{\text{excess NaOH}(aq)} P$ $\text{Ba(NO}_3)_2(aq) \xrightarrow{\text{sodium carbonate solution}} Q \xrightarrow{\text{excess HCl}(aq)} R \xrightarrow{\text{excess NaOH}(aq)} S$ $M$, $N$ and $P$ are magnesium compounds. $Q$, $R$ and $S$ are barium compounds. How many of $M$, $N$, $P$, $Q$, $R$ and $S$ form white precipitates?
- A2
- B3
- C4
- D5