For the group III separation, which of the following statements are correct?

A $NH X_{4} Cl$ raises the pH of the solution to above 12, which is needed for the precipitation.
BThe low $[OH X^{-}]$ prevents precipitation of $Mg (OH) X_{2}$ and $Mn (OH) X_{2}$ .
CExcess $NH X_{4} X^{+}$ from $NH X_{4} Cl$ keeps $[OH X^{-}]$ low through the common ion effect.
D $Fe (OH) X_{3}$ and $Al (OH) X_{3}$ still precipitate because their $K_{s p}$ values are extremely small.

Answer: B, C, D

NH X_{4} OH NH X_{4} X^{+} + OH X^{-}

is suppressed by

NH X_{4} X^{+}

, so the solution is only mildly basic (an ammonia/ammonium buffer, pH about 9), not above 12. The ionic products of

Mg (OH) X_{2}

and

Mn (OH) X_{2}

stay below their

K_{s p}

, whereas

Fe (OH) X_{3}

and

Al (OH) X_{3}

exceed theirs. Statement 4 is therefore false.