Choose the Incorrect statement from the following:

The correct answer is Option (3) → Ionisation enthalpy of Zn²⁺ is lower than that of Cu²⁺.

Here, “ionisation enthalpy of Mⁿ⁺” means the energy needed to remove the next electron from that ion, so for M²⁺ it is the third ionisation enthalpy of the metal. This value is especially high when the electron has to come out of a stable half-filled d⁵ or completely filled d¹⁰ set. It is comparatively low when losing the electron leaves such a stable set behind.

• Option (1) Ionisation enthalpy of Mn⁺ is lower than that of Cr⁺. — A correct statement (Mn⁺ 1509 < Cr⁺ 1592 kJ mol⁻¹). \( \ce{Cr^{+}} \) is 3d⁵ and its next electron comes out of a half-filled set; \( \ce{Mn^{+}} \) is 3d⁵4s¹ and loses its 4s electron easily.

• Option (2) Ionisation enthalpy of Fe²⁺ is lower than that of Mn²⁺. — A correct statement (Fe²⁺ 2957 < Mn²⁺ 3248 kJ mol⁻¹). \( \ce{Mn^{2+}} \) is the stable half-filled 3d⁵; \( \ce{Fe^{2+}} \) is 3d⁶ and becomes 3d⁵ by losing one electron.

• Option (3) Ionisation enthalpy of Zn²⁺ is lower than that of Cu²⁺. — The incorrect statement (Zn²⁺ 3833 > Cu²⁺ 3554 kJ mol⁻¹). \( \ce{Zn^{2+}} \) is 3d¹⁰, so its next electron must come out of a completely filled d set; \( \ce{Cu^{2+}} \) is 3d⁹.

• Option (4) Ionisation enthalpy of V²⁺ is lower than that of Cr²⁺. — A correct statement (V²⁺ 2828 < Cr²⁺ 2987 kJ mol⁻¹). \( \ce{V^{2+}} \) is 3d³ and \( \ce{Cr^{2+}} \) is 3d⁴; Cr has one more proton and holds its electrons more strongly.

NCERT (2026-27 edition):
Ionisation Enthalpies – …