JEE Main 2026 — Chemical Bonding and Molecular Structure Question with Solution

Species with the same number of valence electrons and the same skeletal structure generally have similar Lewis dot structures (isoelectronic species).

For pair A: ${\text{SO}}_3^{2-}$ has $6+3(6)+2=26$ valence electrons. ${\text{CO}}_3^{2-}$ has $4+3(6)+2=24$ valence electrons. Since they have different numbers of valence electrons, they do not have similar Lewis dot structures (${\text{SO}}_3^{2-}$ has a lone pair on the central atom and is pyramidal, while ${\text{CO}}_3^{2-}$ has no lone pair on the central atom and is trigonal planar).

For pair B: ${\text{O}}_2^{2-}$ has $2(6)+2=14$ valence electrons. ${\text{F}}_2$ has $2(7)=14$ valence electrons. Both have a single bond and three lone pairs on each atom, so they have similar Lewis dot structures.

For pair C: ${\text{CN}}^{-}$ has $4+5+1=10$ valence electrons. $\text{CO}$ has $4+6=10$ valence electrons. Both have a triple bond and one lone pair on each atom, so they have similar Lewis dot structures.

For pair D: ${\text{NH}}_3$ has $5+3(1)=8$ valence electrons. ${\text{H}}_3{\text{O}}^{+}$ has $6+3(1)-1=8$ valence electrons. Both have three single bonds and one lone pair on the central atom, so they have similar Lewis dot structures.

For pair E: ${\text{MnO}}_4^{2-}$ has $7+4(6)+2=33$ valence electrons. ${\text{CrO}}_4^{2-}$ has $6+4(6)+2=32$ valence electrons. Since they have different numbers of valence electrons (${\text{MnO}}_4^{2-}$ has an unpaired electron), they do not have similar Lewis dot structures.

Thus, pairs A and E do not have similar Lewis dot structures.

Answer: A and E