Concept:Nitrogen is essential for chlorophyll and protein synthesis, so its deficiency primarily affects leaf colour.
Explanation:Chlorophyll gives leaves their green colour and contains nitrogen.
When nitrogen is deficient, chlorophyll production decreases.
This results in a uniform yellowing of leaves, especially older ones.
Slow growth and smaller leaves and fruits also occur, but the most visible and typical symptom is leaf yellowing.
Purple colouration indicates phosphorus deficiency, not nitrogen deficiency.
Answer:B. yellowing of leaves.