- Molecules that are NOT isoelectronic to 𝐍𝐎𝟐 +ion are
(A) CO2 and N3 −
(B) NCO−and H3BCN −
(C) BO2 −and H3CC ≡ CH
(D) OF2 and O3 −
NO₂⁺ has 16 valence electrons (N: 5 + 2×O: 12 – 1 charge), so isoelectronic species must also have 16 valence electrons. The correct option identifies molecules without this count.
Option Analysis
(A) CO₂ and N₃⁻
CO₂ totals 22 electrons (C: 4 + 2×6), while N₃⁻ has 22 (3×5 +1).[code] Neither matches 16, but both are isoelectronic to each other, not NO₂⁺.
(B) NCO⁻ and H₃BCN⁻
NCO⁻ (cyanate) sums to 16 (N:5 + C:4 + O:6 +1). H₃BCN⁻ totals 16 (3H:3 + B:3 + C:4 + N:5 +1). Both match NO₂⁺.
(C) BO₂⁻ and H₃CC≡CH
BO₂⁻ has 18 electrons (B:3 + 2×6 +1). H₃CC≡CH (propyne, C₃H₄) totals 16 (3C×4 + 4H×1).[code_file] BO₂⁻ does not match.
(D) OF₂ and O₃⁻
OF₂ has 20 electrons (O:6 + 2F×7). O₃⁻ totals 19 (3×6 +1). Neither matches.
Answer: (C) BO₂⁻ lacks 16 electrons.
NO₂⁺ ion serves as a benchmark in isoelectronic comparisons due to its linear structure and 16 valence electrons, vital for CSIR NET chemistry questions on molecular orbitals and bonding. Isoelectronic species share identical electron counts, influencing similar geometries despite atomic differences.
Valence Electron Calculation Method
Count atomic valence electrons, adjust for charge: subtract for cations, add for anions. For NO₂⁺: 5 (N) + 12 (2O) -1 =16.
Detailed Option Breakdown
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CO₂ (22e⁻), N₃⁻ (22e⁻): Both exceed 16; isoelectronic pair but not with NO₂⁺.
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NCO⁻ (16e⁻), H₃BCN⁻ (16e⁻): Match perfectly.
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BO₂⁻ (18e⁻), H₃CC≡CH (16e⁻): BO₂⁻ fails the count.[code_file]
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OF₂ (20e⁻), O₃⁻ (19e⁻): No match.
CSIR NET Exam Tip
Practice electron tallying for ions like NO₂⁺, CO₂ in bonding units; option (C) tests partial mismatches.
