Question

Arrange the following in the order of their increasing first ionisation energies.
$(Sc,Cr,Cu$ and $Zn)$

• A. $Sc<Cr<Cu<Zn$
• B. $Cr<Sc<Cu<Zn$
• C. $Sc<Cr<Zn<Cu$
• D. $Sc<Cu<Cr<Zn$

Answer 1

The correct option is A $Sc<Cr<Cu<Zn$

As we move along the first transition series, effective nuclear charge as well as screening effect increases. From $Sc$ to $Cr$, effective nuclear charge overpowers the screening effect and ionization energy increases. From $Mn$ to $Cu$, screening effect balances the effective nuclear charge and hence ionisation energy remains nearly the same. From $Cu$ to $Zn$, ionisation energy increases due to $(n-1)d^{10}n{s}^2$ configuration.
Therefore, correct order of ionisation energy is: $Sc<Cr<Cu<Zn$