What is the general formula of the ions formed by alkaline earth metals?

The cheap compound having a high melting point used in a furnace is

Which element from the following exhibits a common oxidation state of $+2$?

Assertion $(A)$: $Be$ and $Mg$ do not impart any colour to the flame.
Reason $(R)$: The electrons in them are too strongly bound to get excited by the energy of the flame.
The correct option among the following is:

Which of the following elements does not react with water?

$A$ chemistry student wants to identify the metal ion in a salt. They make a paste of the salt with concentrated $HCl$ on a clean platinum wire loop. If they take a small amount of this paste and place it in a non-luminous flame,it produces a green flame. Which metal is present?