Which among the following species has unequal bond lengths?

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Unequal bond lengths occur when bonds are in different environments (different positions in the molecule).

Step 1 — Analyse each species:

: Tetrahedral, all 4 Si–F bonds equivalent → equal bond lengths ✗

: See-saw geometry (sp³d). S has 4 bonds + 1 lone pair:
- 2 axial S–F bonds (90° from lone pair)
- 2 equatorial S–F bonds (120° from lone pair)
- Axial bonds are longer/weaker than equatorial bonds → unequal bond lengths ✓

: Square planar, all 4 Xe–F bonds equivalent → equal bond lengths ✗

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