When a plant shows reddish leaves, the soil is deficient in

Analyze the question: The question asks which mineral deficiency causes reddish (purplish-red) leaves in plants.

Concept: Plants need mineral nutrients, and each deficiency shows a typical symptom:

• Nitrogen: Yellowing (chlorosis) of older leaves first, and stunted growth.
• Phosphorus: Leaves turn dark green with reddish or purplish tints. This happens because phosphorus shortage causes anthocyanin pigments (red/purple) to accumulate. Growth is stunted and roots are poorly developed.
• Iron: Yellowing of young leaves, with the veins staying green (interveinal chlorosis).
• Calcium: Poor growth of young leaves and root tips, and distorted or hooked young leaves.
• Sulphur: General yellowing of young leaves.

Solution:

1. Reddish or purplish leaves point to anthocyanin build-up.
2. This is the classic sign of phosphorus deficiency.
3. Nitrogen deficiency can sometimes cause reddish tints in a few plants, but its typical sign is pale yellow-green leaves. The standard textbook answer for reddish or purple leaves is phosphorus.

Answer: D. phosphorus

Exam tip: Remember "P for Purple". Phosphorus deficiency gives purple/red leaves, while N for "Not green enough" gives yellow leaves (nitrogen deficiency).