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$Al_2O_3$ can be converted to anhydrous $AlCl_3$ by heating :-
A
$Al_2O_3$ with HCl gas
B
$Al_2O_3$ with NaCl in solid state
C
A mixture of $Al_2O_3$ and carbon in dry $Cl_2$ gas
D
$Al_2O_3$ with $Cl_2$ gas
Detailed Solution
$Al_2O_3$ is a very stable oxide because aluminium has a strong affinity for oxygen.
Chlorine alone cannot displace the oxygen, and heating with HCl gas or solid NaCl does not give the anhydrous chloride.
When a mixture of alumina and carbon is heated in a current of dry chlorine, the carbon removes the oxygen as CO and the chlorine combines with the aluminium:
$Al_2O_3 + 3C + 3Cl_2 \xrightarrow{\Delta} 2AlCl_3 + 3CO$
The anhydrous $AlCl_3$ formed sublimes and is collected.
The chlorine must be dry, because $AlCl_3$ is readily hydrolysed by moisture.
So anhydrous $AlCl_3$ is obtained by heating a mixture of $Al_2O_3$ and carbon in dry $Cl_2$ gas.
Chlorine alone cannot displace the oxygen, and heating with HCl gas or solid NaCl does not give the anhydrous chloride.
When a mixture of alumina and carbon is heated in a current of dry chlorine, the carbon removes the oxygen as CO and the chlorine combines with the aluminium:
$Al_2O_3 + 3C + 3Cl_2 \xrightarrow{\Delta} 2AlCl_3 + 3CO$
The anhydrous $AlCl_3$ formed sublimes and is collected.
The chlorine must be dry, because $AlCl_3$ is readily hydrolysed by moisture.
So anhydrous $AlCl_3$ is obtained by heating a mixture of $Al_2O_3$ and carbon in dry $Cl_2$ gas.