Carotenoids are pigments and have central double bond.

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Carotenoids are pigments because their color comes from a long, conjugated system of alternating double and single bonds that allows electrons to delocalize across the chain. This delocalization determines which wavelengths of light are absorbed; the more extended the conjugation, the lower the energy of the absorbed photons, shifting color toward longer wavelengths (orange to red) and giving carotenoids their characteristic hues. The central double bond is part of this conjugated chain and helps define the exact light absorption pattern—altering the chain length or placement of double bonds changes the visible color. The other options describe different types of biomolecules by their usual bonds (glycosidic in carbohydrates, peptide in proteins, ester in lipids) rather than the distinctive conjugated polyene structure that makes carotenoids pigments.