Which of the following alkaline earth metal nitrides is volatile?

$A$ hydrated colorless solid $(A)$ is water soluble and finds use in medicine as a purgative. When a solution of $(A)$ is treated with ammonium phosphate,a white precipitate is formed. $(A)$ gives a pink mass in the cobalt nitrate cavity test. What is $(A)$?

Which of the following elements does not exhibit variable valency?

Why do beryllium and magnesium not impart colour to the flame in the flame test?

In India,during wedding ceremonies,a green flame is observed in fireworks. Which of the following elements is responsible for this?

Which of the following chlorides is covalent and soluble in ether?