JEE Main 2025 Apr 7 Shift 2, Chemistry Q12: Introduction And Nomenclature

JEE Main2025Apr 7, Shift 2Chemistry

Match List-I with List-II

List-I Complex	List-II Primary valency and Secondary valency
(A) [Co(en) $_{2}$ Cl $_{2}$ ]Cl	(I) 3, 6
(B) [Pt(NH $_{3}$ ) $_{2}$ Cl(NO $_{2}$ )]	(II) 3, 4
(C) Hg[Co(SCN) $_{4}$ ]	(III) 2, 6
(D) [Mg(EDTA)] $^{2 -}$	(IV) 2, 4

Choose the correct answer from the options given below :

A
(A)-(III), (B)-(I), (C)-(II), (D)-(IV)
B
(A)-(I), (B)-(IV), (C)-(II), (D)-(III)
C
(A)-(I), (B)-(III), (C)-(II), (D)-(IV)
D
(A)-(II), (B)-(III), (C)-(IV), (D)-(I)

Solution

The primary valency of a complex equals the oxidation state of the central metal, while the secondary valency equals its coordination number.

In [Co(en) $_{2}$ Cl $_{2}$ ]Cl, cobalt balances one Cl $^{-}$ outside the coordination sphere plus two Cl $^{-}$ inside, giving oxidation state +3; en is bidentate, so coordination number $= 2 (2) + 2 (1) = 6$ . (A): 3, 6.

In [Pt(NH $_{3}$ ) $_{2}$ Cl(NO $_{2}$ )], the complex is neutral, so Pt's oxidation state balances one Cl $^{-}$ and one NO $_{2}^{-}$ , giving +2; coordination number = 2 (NH $_{3}$ ) + 1 (Cl) + 1 (NO $_{2}$ ) = 4. (B): 2, 4.

In Hg[Co(SCN) $_{4}$ ], Hg is present as Hg $^{+}$ , balancing a singly charged complex anion [Co(SCN) $_{4}$ ] $^{-}$ ; in this anion cobalt shows oxidation state +3 (giving primary valency 3), with four monodentate SCN $^{-}$ ligands giving secondary valency (coordination number) 4. (C): 3, 4.

In [Mg(EDTA)] $^{2 -}$ , Mg carries oxidation state +2 (primary valency 2), and the hexadentate EDTA $^{4 -}$ ligand occupies all six coordination positions, giving secondary valency 6. (D): 2, 6.

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JEE Main 2025 Apr 7 Shift 2, Chemistry Q12: Introduction And Nomenclature

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