Question

Which has lowest and highest first ionisation enthalpy in 3d series?

• A. $Sc\text{and}Zn$
• B. $Zn\text{and}Sc$
• C. $Cu\text{and}Zn$
• D. $Cr\text{and}Zn$

Answer 1

The correct option is A $Sc\text{and}Zn$

$\text{Electronic configuration of Sc}:\left[Ar\right]3d^{1}4s^2$

Across a period, the number of protons in the nucleus increases, due to which, the effective nuclear charge also increases and thus, it is difficult to remove an electron from the outermost shell.
Hence, $Sc$ will have the least nuclear charge and first ionisation enthalpy compare to others in 3d-series.

$\text{Electronic configuration of Zn}:\left[Ar\right]3d^{10}4s^2$

In Zn, the orbitals are fully filled and are stable so abstraction of electron from its orbital is difficult compare to the other elements in the 3d-series.
Hence, it has the highest first ionisation enthalpy in 3d-series.

$1^{st}I.E\text{of Sc has}631kJmo{l}^{-1}$
$1^{st}I.E1\text{of Zn has}906kJmo{l}^{-1}$

Hence, option (a) is correct.