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A canonical (resonance) contributing structure is comparatively more stable when:

1. it involves cyclic delocalization of (4n + 2) pi-electrons rather than acyclic delocalization of (4n + 2) pi-electrons.
2. it involves cyclic delocalization of (4n) pi-electrons rather than acyclic delocalization of (4n) pi-electrons.
3. a +ve charge resides on a more electronegative atom rather than on a less electronegative atom, the atoms being in the same period.
4. a -ve charge resides on a more electronegative atom rather than on a less electronegative atom, the atoms being in the same period.

Correct answer: it involves cyclic delocalization of (4n + 2) pi-electrons rather than acyclic delocalization of (4n + 2) pi-electrons.

Solution

Aromatic (4n+2) cyclic delocalization confers special stability, so such a canonical structure is more stable than the acyclic analogue. A negative charge (not positive) is stabilized on a more electronegative atom, so option 1 is the universally correct statement.

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