Sorel's cement is

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

Choose the correct statement from the following:
$(i)$ Beryllium is not readily attacked by acids because of the presence of an oxide film on the surface of the metal.
$(ii)$ $BeO$ is an amphoteric oxide.
$(iii)$ Beryllium exhibits coordination number more than four.
$(iv)$ Beryllium oxide is purely acidic in nature.

The compound formed when gypsum is dissolved in aqueous ammonium sulphate solution is:

Which of the following is the correct order of basic strength?

Magnesia is