Explanation:

- Calcium: Primarily aids in cell wall formation and stability. It helps prevent physiological disorders but doesn’t directly boost resistance to pests.

- Phosphorus: Essential for energy transfer and genetic material synthesis in plants but is not specifically linked to disease or pest resistance.

- Nitrogen: Critical for plant growth and protein synthesis, but excessive nitrogen can sometimes lead to more pest issues.

- Potassium: ? Enhances overall plant vigor and strengthens plant tissues, making them more resistant to disease and pest attacks. It plays a key role in activating enzymes and enhancing photosynthesis.

Correct Answer: Potassium