$Cl^-$ has a negligible basicity. Conjugate acid: $HCl$, which is a strong acid.
Work Step by Step
$Cl^-(aq) + H_2O(l) --> HCl(aq) + OH^-(aq)$ As we can observe, $HCl$ is the conjugate acid of $Cl^-$. Since $Cl^-$ has a insignificant base, the conjugate acid will be strong.