Plaster of Paris is hardened by

The fluoride which is most soluble in water is

Which of the following compounds has a lattice energy value lower than its hydration energy?

Thermal stability of $BaCO_3, CaCO_3, SrCO_3$ and $MgCO_3$ decreases in the order of :

Chemical $A$ is used for the removal of temporary hardness of water. Compound $A$ reacts with $Na_2CO_3$ to produce caustic soda. When $CO_2$ gas is passed through $A$,it turns milky. What is the chemical formula of $A$?

Chemical $A$ is used for water softening to remove temporary hardness. $A$ reacts with $Na_2CO_3$ to generate caustic soda. When $CO_2$ is bubbled through $A$,it turns cloudy. What is the chemical formula of $A$?