Given below are two statements : Statement I : The first ionization enthalpy of Cr is lower than that of Mn . Statement II : The second and third ionization enthalpies of Cr are higher than those of Mn. In the light of the above statements, choose the correct answer from the options given below :
D. Statement I is true but Statement II is false
Statement I: The electronic configuration of Cr is [Ar] 3d^5 4s^1 and Mn is [Ar] 3d^5 4s^2. For Cr, the first electron is removed from 4s^1, while for Mn, it is removed from a stable fully filled 4s^2 subshell. Additionally, Mn has a higher nuclear charge. Thus, the first ionization enthalpy (IE_1) of Cr (653 kJ/mol ) is lower than that of Mn (717 kJ/mol ). Statement I is true. Statement II: For the second ionization enthalpy (IE_2), Cr^+ has configuration [Ar] 3d^5 (stable half-filled) and Mn^+ has [Ar] 3d^5 4s^1. Removing an electron from the stable 3d^5 configuration of Cr^+ requires more energy than removing it from the 4s^1 of Mn^+. Thus, IE_2 of Cr (1592 kJ/mol ) is higher than Mn (1509 kJ/mol ). For the third ionization enthalpy (IE_3), Cr^ 2+ is [Ar] 3d^4 and Mn^ 2+ is [Ar] 3d^5. Removing an electron from the stable half-filled 3d^5 configuration of Mn^ 2+ requires significantly more energy than from the 3d^4 of Cr^ 2+ . Thus, IE_3 of Mn (3248 kJ/mol ) is higher than Cr (2987 kJ/mol ). Since IE_3 of Cr is lower than Mn, Statement II is false.
Related: Chemistry — d and f Block Elements · All PYQ Banks