Question

Among the following transition elements, which one has the highest second ionisation energy?

$\left(\right.i\left.\right) \, V \, \left(Z = 23\right) \, \, \left(\right.ii\left.\right) \, Cr \, \left(Z = 24\right) \, \, \left(\right.iii\left.\right) \, Mn \, \left(Z = 25\right) \, \, \left(\right.iv\left.\right) \, Ti \, \left(Z = 22\right)$

• A. (i)
• B. (ii)
• C. (iii)
• D. (iv)

Answer 1

Answer: (B)

The general trend observed in the second ionisation enthalpy of $3d-$ series elements is that as we move from left to right in the period, the ionisation energy increases. But, $Cr$ and $Zn$ are exceptions to this trend. The value of second ionisation energy for $Cr$ is more than $Mn$ . This can be explained based on the electronic configuration of their $M^{+}$ ions:

$\_{24}^{}Cr_{}^{+}=\left[Ar\right]3d^{5}$ and $\_{25}^{}Mn_{}^{+}=\left[Ar\right]3d^{5}4s^{1}$

$Cr^{+}$ has a stable electronic configuration because of half-filled $d-$ subshell. Thus removing an electron from it is difficult. Therefore, $Cr$ has the highest second ionisation energy among the given elements.

The correct order for second ionisation energy for the given elements is $Ti < V < Mn < Cr$ .