Strong heating of $MgCl X_{2} \cdot 6 H X_{2} O$ gives $MgO$ (or basic chloride) and $HCl$ instead of anhydrous $MgCl X_{2}$ . The underlying reason is that

Athe small, doubly charged $Mg X^{2 +}$ strongly polarises coordinated water, favouring hydrolysis with loss of $HCl$
B $MgCl X_{2}$ sublimes on heating
C $Cl X^{-}$ is oxidised by the water of crystallisation
D $Mg X^{2 +}$ is reduced to $Mg$ by water

Answer: A

Mg X^{2 +}

has a high ionic potential and withdraws electron density from the O-H bonds of the coordinated water, making them easy to cleave. Proton transfer to

Cl X^{-}

then releases

HCl

and leaves an oxide or hydroxide chloride. No redox change occurs, and

MgCl X_{2}

does not sublime.