Correct option is D
✅ (d) Nitrogen: • Nitrogen deficiency weakens plants, reducing chlorophyll, protein synthesis, and natural defense mechanisms. • As a result, plants become more vulnerable to fungal and bacterial pathogens.
❌ (a) Silicon: • Provides mechanical strength and helps resist pests, but deficiency doesn’t directly increase fungal susceptibility as much as N.
❌ (b) Nickel: • Involved in enzyme systems but not directly linked with fungal resistance.