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JEE Advanced levelSingle correct optionDifficulty 3 of 3cb200

Assertion (A): Molten $NaCl$ conducts electricity but molten $AlCl X_{3}$ does not. Reason (R): $AlCl X_{3}$ is covalent because $Al X^{3 +}$ is large and has a low charge.

ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is not the correct explanation of A
CA is true but R is false
DA is false but R is true

Answer: C

Molten

NaCl

contains mobile

Na X^{+}

and

Cl X^{-}

ions.

AlCl X_{3}

is largely covalent (molecular, as

Al X_{2} Cl X_{6}

), so it has almost no free ions in the melt; A is true. The reason is wrong because

Al X^{3 +}

is small and highly charged, giving high polarising power; R is false.

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