Given below are two statements: Statement I: Among Zn, Mn, Sc and Cu, the energy required to remove the third valence electron is highest for Zn and lowest for Sc. Statement II: The correct order of the following complexes in terms of CFSE is [Co(H_2 O)_6]^ 2+ In the light of the above statements, choose the correct answer from the options given below:
A. Both Statement I and Statement II are true
Statement I: The third ionization energy (IE_3) corresponds to the removal of the third valence electron. Let us look at the electronic configurations of the divalent cations for the given metals: Sc^ 2+ : [Ar] 3d^ 1 Mn^ 2+ : [Ar] 3d^ 5 Cu^ 2+ : [Ar] 3d^ 9 Zn^ 2+ : [Ar] 3d^ 10 For Sc, removing the third electron involves taking it from the 3d^ 1 state, which results in a highly stable noble gas core ([Ar]). Hence, Sc has the lowest IE_3. For Zn, the third electron must be removed from a completely filled, highly stable 3d^ 10 subshell. Combined with its high effective nuclear charge (Z_ eff ) across the 3d series, Zn requires the highest energy for the removal of the third electron. Thus, Statement I is true. Statement II: The Crystal Field Stabilization Energy (CFSE) depends on the magnitude of the crystal field splitting energy ( _o), which in turn depends on the oxidation state of the central metal ion and the strength of the ligand. 1. Oxidation state: A higher oxidation state on the central metal ion leads to a larger _o. Therefore, the splitting for Co^ 3+ complexes is significantly greater than for Co^ 2+ complexes. This makes the CFSE of [Co(H_2O)_6]^ 3+ greater than that of [Co(H_2O)_6]^ 2+ . 2. Nature of the ligand: Ethylenediamine (en) is a strong field bidentate ligand, whereas H_2O is a weak field ligand. According to the spectrochemical series, en causes a much larger splitting than H_2O. Thus, the _o and CFSE for [Co(en)_3]^ 3+ are greater than those for [Co(H_2O)_6]^ 3+ . The overall order of CFSE is: [Co(H_2O)_6]^ 2+ Thus, Statement II is true. Since both statements are correct, the correct option is (1). Answer: Both Statement I and Statement II are true
Related: Chemistry — Classification of Elements and Periodicity in Properties · All PYQ Banks