Assertion: $HCl$ is a covalent compound but it conducts electricity in its aqueous state. Reason: In aqueous solution $HCl$ ionises to $H^{+}$ and $C{l}^{-}$ ions which are responsible for electrical conductivity.

The correct option is A Both assertion and reason are correct and reason is the correct explanation for assertion.
Ionic solutions have the capability to conduct electricity. Therefore, $HCl$ in an aqueous solution can conduct electricity because it forms ions. Pure $HCl$ does not conduct electricity in water because there are no free ions such as $H^{+}$ and $C{l}^{-}$ ions as they are strongly held by electrostatic force.