Why first ionisation enthalpy of $\mathrm{Cr}$ is lower than that of $\mathrm{Zn}$ ?
Why first ionisation enthalpy of $\mathrm{Cr}$ is lower than that of $\mathrm{Zn}$ ?
${ }_{24} \mathrm{Cr}:[\mathrm{Ar}] 3 d^{5} 4 s^{1} \quad{ }_{30} \mathrm{Zn}:[\mathrm{Ar}] 3 d^{10} 4 s^{2}$
After loss of one element, $\mathrm{Cr}$ attains stable $\left(d^{5}\right)$ configuration while in zinc, the electron has to be removed from $4 s$ orbital. Hence, first ionization enthalpy of $\mathrm{Cr}$ is lower than $\mathrm{Zn}$.
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