Select the incorrect statement

Milk of magnesia which is used as antacid, chemically is $\left({\mathrm{MgCl}}_2+\mathrm{MgO}\right)$

$\text{ Mortar is a mixture of }\mathrm{Ca}(\mathrm{OH}{)}_2\text{, Silica and water. }$

$\text{ Plaster of Paris is }{\mathrm{CaSO}}_4\cdot \frac{1}{2}{\mathrm{H}}_2\mathrm{O}$

Plaster of Paris when mixed with correct amount of water sets into a solid mas$ due to the formation of ${\mathrm{CaSO}}_4\cdot 2{\mathrm{H}}_2\mathrm{O}$