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NEET Chemistry: Resonance Practice Questions

15 free multiple-choice questions on Resonance (Chemical Bonding and Molecular Structure) for NEET Chemistry, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. When comparing two resonance structures for a species, the structure with the lower energy is identified as the:

    • AMinor contributing structure
    • BKinetic structure
    • CMajor contributing structure
    • DThermodynamically preferred structure
    Show answer & explanation

    Correct answer: D — Thermodynamically preferred structure

    The structure corresponding to the lower energy level is the thermodynamically preferred and most stable resonance contributor.

  2. Q2. In the resonance structures of the nitrate ion (NO₃⁻), the negative charge is delocalized over the three oxygen atoms. This delocalization primarily results in which property of the ion?

    • AThe presence of a formal charge on the nitrogen atom.
    • BIncreased localized bond strength between N and O.
    • CA purely localized bond angle structure.
    • DEqual sharing of the electron density among all oxygen atoms.
    Show answer & explanation

    Correct answer: D — Equal sharing of the electron density among all oxygen atoms.

    Delocalization of pi electrons (or lone pairs) across multiple atoms leads to an equal sharing of electron density among those atoms, which is reflected by the delocalization of the charge.

  3. Q3. How many resonance structures can be represented for the carbonate ion ion (CO₃²⁻)?

    • A1
    • B4
    • C2
    • D3
    Show answer & explanation

    Correct answer: B — 4

    The carbonate ion has 3 C-O bonds, allowing the double bond character to be delocalized over the three oxygen atoms, resulting in three major resonance structures.

  4. Q4. The concept of resonance primarily helps in determining the:

    • ANumber of valence electrons in the molecule.
    • BSpecific bond angle of a localized structure.
    • CRelative stability among different possible structures.
    • DExact bond length of a single bond.
    Show answer & explanation

    Correct answer: C — Relative stability among different possible structures.

    Resonance theory is used to compare the stability of various contributing structures to find the most stable resonance form.

  5. Q5. Which of the following molecules exhibits greater stability due to resonance effects?

    • ACyclohexene
    • BBenzene
    • C1,3-Butadiene
    • DPropene
    Show answer & explanation

    Correct answer: B — Benzene

    Benzene is the most stable aromatic compound because the delocalization of pi electrons across the ring results in a lower overall energy state compared to its non-aromatic isomers.

  6. Q6. Which of the following statements correctly describes the concept of resonance in organic molecules?

    • AResonance implies that all resonance structures have the same bond order.
    • BResonance occurs only in molecules containing triple bonds.
    • CResonance involves the delocalization of pi electrons over a conjugated system.
    • DResonance is only applicable to molecules containing only single bonds.
    Show answer & explanation

    Correct answer: C — Resonance involves the delocalization of pi electrons over a conjugated system.

    Resonance describes the delocalization of pi (π) electrons across a system of adjacent atoms, which is the basis for forming resonance structures.

  7. Q7. Which resonance structure is considered the most stable for the nitrite ion (NO₂⁻)?

    • AStructure where the formal charge is distributed equally across all oxygen atoms.
    • BStructure where the double bond is localized between N and O₁.
    • CStructure where the double bond is localized between N and O₂.
    • DStructure where the bond order is exactly 2.5.
    Show answer & explanation

    Correct answer: C — Structure where the double bond is localized between N and O₂.

    The most stable resonance structure is the one where the formal charges are minimized. In the case of NO₂⁻, the structure where the double bond is localized between N and O₂ (where O₁ has a formal charge of -1 and O₂ has a formal charge of 0, assuming N has a formal charge of +1) is preferred, minimizing charge separation.

  8. Q8. Which statement correctly describes the primary role of resonance in determining the stability of a molecule?

    • AResonance allows for the delocalization of π electrons, leading to lower energy
    • BResonance increases the energy of the molecule
    • CResonance leads to the formation of stronger sigma bonds
    • DResonance only affects bond lengths but not energy
    Show answer & explanation

    Correct answer: A — Resonance allows for the delocalization of π electrons, leading to lower energy

    Resonance occurs due to the delocalization of π electrons. This delocalization spreads the charge over multiple atoms, resulting in a more stable, lower-energy state for the molecule.

  9. Q9. In the resonance structures of benzene, which statement is true regarding the bond lengths?

    • AThe C-C bonds alternate between single and double bonds.
    • BThe bond lengths are intermediate between a single and a double bond in each structure.
    • CAll C-C bonds are of equal length.
    • DAll C-C bonds in the resonance structures are equal in length.
    Show answer & explanation

    Correct answer: D — All C-C bonds in the resonance structures are equal in length.

    Due to the equal delocalization of pi electrons, the bond order is intermediate between a single bond and a double bond (i.e., 1.5), making all C-C bonds equivalent in length.

  10. Q10. Which of the following pairs of structures represents equivalent bond lengths in a resonance hybrid?

    • AStructures where the number of sigma bonds differs
    • BStructures with different hybridization
    • CStructures with different formal charges
    • DStructures where pi electrons are delocalized over the same number of atoms
    Show answer & explanation

    Correct answer: D — Structures where pi electrons are delocalized over the same number of atoms

    Equivalent bond lengths arise when the pi electrons are delocalized (shared) equally across the entire system of atoms in the resonance hybrid, meaning the environment around the bonding atoms is identical.

  11. Q11. In the resonance hybrid of benzene, the electrons are distributed as:

    • ARestricted to forming only single bonds.
    • BLocalized in specific C-C bonds.
    • CConcentrated only on the sp² hybridized atoms.
    • DDelocalized equally over all six carbon atoms.
    Show answer & explanation

    Correct answer: D — Delocalized equally over all six carbon atoms.

    Benzene exhibits aromatic character due to the delocalization of π electrons over the entire ring. This results in electron density being shared equally across all six carbon atoms, forming the resonance hybrid.

  12. Q12. Which statement is generally true regarding resonance structures of a molecule?

    • AResonance structures only apply to molecules containing triple bonds.
    • BResonance structures represent different possible valid molecular geometries.
    • CResonance structures indicate the actual experimental geometry of the molecule.
    • DThe actual structure is a hybrid of all contributing resonance structures.
    Show answer & explanation

    Correct answer: D — The actual structure is a hybrid of all contributing resonance structures.

    The actual molecular structure is a hybrid (resonance hybrid) of all contributing resonance structures.

  13. Q13. The concept of resonance implies that electrons are delocalized over a region. This delocalization primarily results in which of the following effects on the molecular structure?

    • AStabilization of the molecule and reduced bond energy
    • BIncreased localized bond energies
    • CIncreased localized bond lengths
    • DIncreased molecular rigidity only
    Show answer & explanation

    Correct answer: A — Stabilization of the molecule and reduced bond energy

    Delocalization of electrons leads to a more stable configuration (lower energy), which is the primary thermodynamic outcome of resonance.

  14. Q14. In the context of resonance structures, which structure is generally considered the most physically realistic representation of a bonding system?

    • AThe structure where all atoms are connected by single bonds
    • BThe structure with the maximum number of formal charges
    • CThe structure that minimizes the total formal charge across all atoms
    • DThe structure resulting in the largest number of bond angles
    Show answer & explanation

    Correct answer: C — The structure that minimizes the total formal charge across all atoms

    The most physically realistic structure is the one where the total formal charge is minimized, which corresponds to the most stable resonance structure (the one with the lowest energy).

  15. Q15. The concept of resonance primarily addresses the phenomenon of:

    • AIonization Energy
    • BHypervalency
    • CCrystal Field Splitting
    • DDelocalization of pi electrons
    Show answer & explanation

    Correct answer: D — Delocalization of pi electrons

    Resonance is the concept describing the delocalization of pi electrons over a conjugated system, which is crucial for understanding the stability and bonding in molecules.

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