A transition metal M is chosen from the group Ti , V , Cr , and Mn such that it has the highest second ionisation enthalpy among them. The spin-only magnetic moment of the M ³⁺ ion is:

Step-by-step solution

The second ionisation enthalpy is the energy required to remove an electron from the M ⁺ ion. The electronic configurations of the +1 ions are: Ti ⁺ : [ Ar ] 3 d ² 4 s ¹ V ⁺ : [ Ar ] 3 d ³ 4 s ¹ Cr ⁺ : [ Ar ] 3 d ⁵ Mn ⁺ : [ Ar ] 3 d ⁵ 4 s ¹ For chromium, the removal of the second electron disrupts the highly stable half-filled 3 d ⁵ configuration. Therefore, Cr has the highest second ionisation enthalpy among the given metals. Thus, M is Cr . The M ³⁺ ion is Cr ³⁺ , which has the electronic configuration [ Ar ] 3 d