Which statements about magnesium ammonium phosphate, formed in the group VI test, are correct?

AIt is precipitated only when $NH X_{4} X^{+}$ and $NH X_{3}$ are present, i.e. in ammoniacal medium.
BIt dissolves in dilute acetic acid and in mineral acids.
CIt is a yellow solid.
DStrong ignition converts it into magnesium pyrophosphate, $Mg X_{2} P X_{2} O X_{7}$ .

Answer: A, B, D

The phosphate precipitates

Mg X^{2 +}

as the white crystalline salt

Mg (NH X_{4}) PO X_{4}

only when ammonium ions and ammonia are available, and the salt is soluble in acids because phosphate is protonated. Ignition gives

Mg X_{2} P X_{2} O X_{7}

with loss of

NH X_{3}

and water. The salt is white, not yellow.