Which of the following elements shows a high tendency to form peroxide?

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

Beryllium resembles much with

An alkaline earth metal $M$ readily forms water-soluble sulphate and water-insoluble hydroxide. Its oxide $MO$ is very stable to heat and does not have rock-salt structure. $M$ is :-

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 has the highest basic nature?