Which of the following are amphoteric oxides?

Plaster of Paris is represented as

Which of the following magnetic properties is exhibited by the compounds of alkaline earth metals?

$A$ 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 $(A)$?

The white enamel of our teeth is composed of:

Calcium is obtained by which of the following methods?