Which pigment is responsible for red colour of tomato?

Concept: Plant colour comes mainly from three pigment families: chlorophylls (green, used in photosynthesis), carotenoids (fat-soluble pigments ranging from yellow through orange to red — this group includes carotenes and xanthophylls), and anthocyanins (water-soluble flavonoid pigments that give red, purple, or blue shades and are sensitive to the tissue's pH). A given coloured compound belongs to exactly one of these families, and only the compounds present in a tissue govern that tissue's visible colour.

Application: As a tomato ripens, its chloroplasts convert into chromoplasts: chlorophyll breaks down while the carotenoid lycopene builds up to a high concentration. Lycopene strongly absorbs blue-green light and reflects red light, so its accumulation is what turns the fruit from green to deep red.

Cross-check: Comparing each option's pigment family against this pathway:

• Cyanide is not a plant pigment at all; it is a toxic defensive compound found in trace amounts in some plants (e.g. bitter almond, cassava) and plays no part in fruit colouration.

• Xanthophyll is a yellow oxygenated carotenoid (seen in autumn leaves, egg yolk, corn) — it produces yellow tones, not red.

• Anthocyanin is a separate, water-soluble flavonoid pigment that produces the red-purple colours of fruits such as grapes, berries, and red cabbage through a pH-sensitive mechanism; it is not the pigment behind a ripe tomato's colour.

• Only the carotenoid build-up described above matches both the ripening chemistry and the observed red colour of tomato.

Hence, Lycopene is the pigment responsible for the red colour of tomato.