How does Plaster of Paris become hard?

Calcium salts give which colour when put in a flame?

Choose the correct statements from the following:
$(I)$ In vapour phase $BeCl_2$ exists as a chlorobridged dimer.
$(II)$ $BeSO_4$ is readily soluble in water.
$(III)$ $BeO$ is completely basic in nature.
$(IV)$ $BeCO_3$ being unstable, is kept in an atmosphere of $CO_2$.
$(V)$ $BeCO_3$ is the least soluble among all the carbonates of group $2$ elements.

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

Electric furnaces are lined with magnesia because

Which of the following is an amphoteric hydroxide?