Resonance — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Resonance structures differ from one another mainly in the arrangement of

• A. electrons, not the positions of atomic nuclei
• B. atomic nuclei only
• C. isotopes only
• D. molecules in space only

Question 2 · difficulty L2 · understanding

The difference in energy between the actual structure and the lowest energy resonance structure for the given compound is

• A. electromeric energy
• B. resonance energy
• C. ionization energy
• D. hyperconjugation energy

Question 3 · difficulty L2 · understanding

The actual structure of a resonance-stabilised species is

• A. a resonance hybrid
• B. a rapid alternation between separate real structures
• C. always identical to the least stable contributor
• D. a mixture of different compounds

Question 4 · difficulty L2 · understanding

Resonance generally stabilises a species because

• A. electron density is delocalised over more than one atom or bond
• B. atoms become heavier
• C. all bonds become ionic
• D. the number of electrons decreases

Question 5 · difficulty L3 · understanding

Identify the species having one $$\pi$$-bond and maximum number of canonical forms from the following :

• A. SO 3
• B. O 2
• C. SO 2
• D. CO$$_3^{2 - }$$

Question 6 · difficulty L3 · understanding

Identify the correct answer.

• A. Three resonance structures can be drawn for ozone
• B. $$\mathrm{BF}_3$$ has non-zero dipole moment
• C. Dipole moment of $$\mathrm{NF}_3$$ is greater than that of $$\mathrm{NH}_3$$
• D. Three canonical forms can be drawn for $$\mathrm{CO}_3^{2-}$$ ion

Question 7 · difficulty L3 · application

In the carbonate ion, the three C-O bonds are experimentally equivalent. This is explained by

• A. resonance delocalisation over three equivalent contributors
• B. one permanent C=O bond and two permanent C-O bonds
• C. rapid breaking of C-O bonds
• D. sp3 carbon with no pi bonding

Question 8 · difficulty L3 · application

Which pair can represent resonance contributors of the same species?

• A. Structures with identical atom connectivity but different pi-electron or lone-pair placement
• B. Structures with different positions of carbon atoms
• C. Two structural isomers
• D. Two compounds with different molecular formulas

Question 9 · difficulty L4 · application

Which resonance contributor generally makes the greatest contribution to a resonance hybrid?

• A. One with complete octets, minimal charge separation and appropriate charge placement
• B. One with the largest number of separated charges
• C. One that violates octet rules unnecessarily
• D. All contributors always contribute equally

Question 10 · difficulty L4 · application

The two N-O bonds in nitrite ion $NO_2^-$ are equal in length. What is the best explanation?

• A. The pi bond and negative charge are delocalised by resonance
• B. One N-O bond is permanently single and the other permanently double
• C. Nitrogen has no valence electrons
• D. The molecule rapidly swaps oxygen atoms