How does Plaster of Paris become hard?

Explain the chemical properties of alkaline earth metals (Group $2$) in detail.

The element playing a significant role in neuromuscular function and interneuronal transmission is:

Which of the following has the highest electrode potential?

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$ :
Assertion $(A)$ : $BeCl_2$ and $MgCl_2$ produce characteristic flame.
Reason $(R)$ : The excitation energy is high in $BeCl_2$ and $MgCl_2$.
In the light of the above statements,choose the correct answer from the option given below :

Enzymes that utilize $ATP$ in phosphate transfer require an alkaline earth metal $(M)$ as the cofactor. $M$ is