Which of the folloWing hydrated salts will not become anhydrous on heating?

${\mathrm{MgCl}}_2, {\mathrm{AlCl}}_3,$and ${\mathrm{SnCl}}_2$ are the chemical formulas for water. ${\mathrm{MgCl}}_2\cdot 6{\mathrm{H}}_2\mathrm{O},{\mathrm{AlCl}}_3\cdot 6{\mathrm{H}}_2\mathrm{O}$, and ${\mathrm{SnCl}}_2\cdot 2{\mathrm{H}}_2\mathrm{O}$cannot be heated only to form anhydrous chloride. As, the ions  ${\mathrm{Mg}}^{2+},{\mathrm{Al}}^{3+}$and ${\mathrm{Sn}}^{2+}$ have more polarisation power.

${\mathrm{MgCl}}_2\cdot 6{\mathrm{H}}_2\mathrm{O}\to \mathrm{MgO}+2\mathrm{HCl}+5{\mathrm{H}}_2$

$2{\mathrm{AlCl}}_3\cdot 6{\mathrm{H}}_2\mathrm{O}\to {\mathrm{Al}}_2{\mathrm{O}}_3+6\mathrm{HCl}+9{\mathrm{H}}_2\mathrm{O}$

${\mathrm{SnCl}}_2\cdot 2{\mathrm{H}}_2\mathrm{O}\to \mathrm{SnO}+2\mathrm{HCl}+{\mathrm{H}}_2\mathrm{O}$.

So, option A, B and C are correct.