Chemistry Q54 – JEE-MAIN 2026

Home Chemistry Chemical BondingQuestion #245

The pairs among

A = [{SO}_{3}^{2 -}, {CO}_{3}^{2 -}]

B = [O_{2}^{2 -}, F_{2}]

C = [{CN}^{-}, CO]

D = [{NH}_{3}, H_{3} O^{+}]

and

E = [{MnO}_{4}^{-}, {CrO}_{4}^{2 -}]

that do not have similar Lewis dot structure are

Clue 1 of 3: Definition of Similar Lewis Structures

Similar Lewis dot structures generally imply that species are isoelectronic (have the same number of valence electrons) and isostructural (have the same arrangement of atoms, bonds, and lone pairs, leading to the same VSEPR geometry).

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Step 1: Analyze Pairs A, B, C, D✦ Active

We determine the total valence electrons, central atom's lone pairs, and VSEPR geometry for each species in pairs A, B, C, and D:

\begin{array}{ll} Pair A: & {SO}_{3}^{2 -} (26 e^{-}, S has 1 lone pair, trigonal pyramidal) \\ {CO}_{3}^{2 -} (24 e^{-}, C has 0 lone pairs, trigonal planar) \\ \Rightarrow Not similar (d i f f e r e n t v a l e n c e e l e c t r o n s, d i f f e r e n t g e o m e t r y, d i f f e r e n t l o n e p a i r s o n c e n t r a l a t o m) . \\ Pair B: & O_{2}^{2 -} (14 e^{-}, O-O single bond, 3 lone pairs on each O, linear) \\ F_{2} (14 e^{-}, F-F single bond, 3 lone pairs on each F, linear) \\ \Rightarrow Similar (i s o e l e c t r o n i c, i d e n t i c a l s t r u c t u r e) . \\ Pair C: & {CN}^{-} (10 e^{-}, C \equiv N triple bond, 1 lone pair on C, 1 lone pair on N, linear) \\ CO (10 e^{-}, C \equiv O triple bond, 1 lone pair on C, 1 lone pair on O, linear) \\ \Rightarrow Similar (i s o e l e c t r o n i c, i d e n t i c a l s t r u c t u r e) . \\ Pair D: & {NH}_{3} (8 e^{-}, N has 3 single bonds, 1 lone pair, trigonal pyramidal) \\ H_{3} O^{+} (8 e^{-}, O has 3 single bonds, 1 lone pair, trigonal pyramidal) \\ \Rightarrow Similar (i s o e l e c t r o n i c, i d e n t i c a l s t r u c t u r e) . \end{array}

Step 2: Analyze Pair E (Transition Metal Oxoanions)○ Expand

For transition metal oxoanions, the most stable Lewis structure often involves multiple bonds to minimize formal charges. We analyze pair E:

\begin{array}{ll} Pair E: & {MnO}_{4}^{-} (32 e^{-}, Mn is in +7 oxidation state) \\ To minimize formal charge, Mn forms 3 Mn=O double bonds and 1 Mn-O single bond. \\ {CrO}_{4}^{2 -} (32 e^{-}, Cr is in +6 oxidation state) \\ To minimize formal charge, Cr forms 2 Cr=O double bonds and 2 Cr-O single bonds. \\ \Rightarrow Not similar (A l t h o u g h b o t h a r e i s o e l e c t r o n i c a n d t e t r a h e d r a l w i t h 0 l o n e p a i r s o n t h e c e n t r a l a t o m, t h e n u m b e r o f d o u b l e b o n d s i n t h e i r m o s t s t a b l e r e s o n a n c e s t r u c t u r e s i s d i f f e r e n t (3 v s 2)) . \end{array}

💡 Teacher's Secret Hint

Remember that for transition metal oxoanions, minimizing formal charges often leads to different numbers of double bonds depending on the oxidation state of the central metal.

Step 3: Identify Dissimilar Pairs○ Expand

Based on the analysis, the pairs that do not have similar Lewis dot structures are A and E.

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Chemistry Question 54 – JEE-MAIN 2026

Clue 1 of 3: Definition of Similar Lewis Structures

🧠 Full Solution Path