Which of the following hydrated chlorides can not be converted into anhydrous chloride only by heating?

${\mathrm{MgCI}}_2·6{\mathrm{H}}_2\mathrm{O}$, ${\mathrm{AlCl}}_3\cdot 6{\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{SnCl}}_2\cdot 2{\mathrm{H}}_2\mathrm{O}$ can not be converted into anhydrous chloride only by heating. Because ${\mathrm{Mg}}^{2+},{\mathrm{Al}}^{3+},{\mathrm{Sn}}^{2+}$ ions have more polarization power

$\begin{array}{r}{\mathrm{MgCl}}_2\cdot 6{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{MgO}}_{\mathrm{g}}+2\mathrm{HCl}+5{\mathrm{H}}_2\\ 2{\mathrm{AlCl}}_9\cdot 6{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{Al}}_2{\mathrm{O}}_3+6\mathrm{HCl}+9{\mathrm{H}}_2\mathrm{O}\\ {\mathrm{SnCl}}_2\cdot 2{\mathrm{H}}_2\mathrm{O}⟶\mathrm{SnO}+2\mathrm{HCl}+{\mathrm{H}}_2\mathrm{O}\end{array}$