Consider and select the correct statement from the following with reference to the ionization enthalpy (IE) values of the 3d series of transition elements:
(A) IE1 of Zn is greater than IE1 of Cu.
(B) IE3 of Mn is greater than IE3 of Fe.
(C) IE2 of Mn is greater than IE2 of Cr.
(D) IE2 of Cr is greater than IE2 of V.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (D) only.
Ionisation enthalpies of the 3d metals rise only slowly across the series, but they show jumps wherever an electron has to be removed from a stable configuration, i.e. a half-filled d5 or completely filled d10 subshell.
(A) IE1 of Zn is greater than IE1 of Cu. — Correct. Zn (Z = 30) is 3d104s2: the electron comes from a filled 4s2 pair with a full 3d10 core. Cu (Z = 29) is 3d104s1 and loses a single 4s electron more easily. IE1: Zn 906 > Cu 745.
(B) IE3 of Mn is greater than IE3 of Fe. — Correct. Mn (Z = 25) is 3d54s2, so \( \ce{Mn^{2+}} \) is 3d5; the third electron must come out of this stable half-filled set. Fe (Z = 26) is 3d64s2, so \( \ce{Fe^{2+}} \) is 3d6 and losing one electron gives the stable 3d5. IE3: Mn 3260 > Fe 2962.
(C) IE2 of Mn is greater than IE2 of Cr. — Incorrect. Cr (Z = 24) is 3d54s1, so \( \ce{Cr^{+}} \) is 3d5 and its second electron comes from the stable d5 set. \( \ce{Mn^{+}} \) is 3d54s1 and loses its 4s electron. IE2: Cr 1592 > Mn 1509.
(D) IE2 of Cr is greater than IE2 of V. — Correct. \( \ce{Cr^{+}} \) (3d5) must lose an electron from the half-filled set, while V (Z = 23, 3d34s2) gives \( \ce{V^{+}} \) (3d34s1), which loses an electron easily. IE2: Cr 1592 > V 1414.
NCERT (2026-27 edition):
Ionisation Enthalpies – …
