Which colour is developed in the solution when alkaline earth metals are dissolved in liquid ammonia?

The setting of Plaster of Paris involves:

Which property of the alkaline earth metals increases with their atomic number?

Which of the following salts is not soluble in water?

$BeO$ reacts with $HF$ in the presence of ammonia to give $[A]$,which on thermal decomposition produces $[B]$ and ammonium fluoride. The oxidation state of $Be$ in $[A]$ is $.....$.

Solubility of the alkaline earth metal sulphates in water decreases in the sequence