Which of the following salts increases the rate of the setting process of Plaster of Paris?

State True or False:
$(1)$ $90 \ g \ Na$ and $170 \ g \ K$ are present in a person with $70 \ kg$ of body weight.
$(2)$ Ionization enthalpy of alkaline earth metals increases on moving top to bottom.
$(3)$ In vapour phase,$BeCl_2$ possesses a polymer-like arrangement.
$(4)$ $CaCO_3$ is used in the preparation of mortar.

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Barium carbonate is insoluble in water and is highly stable.
Reason $R$: The thermal stability of the carbonates increases with increasing cationic size.
Choose the most appropriate answer from the options given below for $A$ and $R$.

What products are obtained when beryllium oxide is treated separately with aqueous $HCl$ and aqueous $NaOH$ solutions respectively?

Gypsum $CaSO_4 \cdot 2H_2O$ on heating to about $120\ ^\circ C$ forms a compound which has the chemical composition represented by :-

Why is beryllium amphoteric in nature?