A fertile soil must contain all the 3 major nutrients namely ______ for basic…

Concept

Plant nutrition rests on a small set of essential elements. Three of them are needed in the largest amounts and are therefore called the primary (major) macronutrients: Nitrogen (N), Phosphorus (P) and Potassium (K) — the familiar "N-P-K" trio. They drive vegetative growth, root and energy transfer, and overall vigour, and a fertile soil must supply all three together. A second group (calcium, magnesium, sulphur) are secondary macronutrients, and the remaining essential elements are micronutrients needed only in trace amounts.

Applying it here

The blank asks for the three MAJOR (primary) nutrients. The only triplet that lists exactly Nitrogen, Phosphorus and Potassium — and nothing else — is the N-P-K set, which matches the definition of the primary macronutrients.

Why the other triplets fail

Each remaining choice swaps in a secondary nutrient or a micronutrient in place of one of the N-P-K members:

• Calcium, Nitrogen, Potassium — calcium is a SECONDARY macronutrient, not one of the three primary ones; phosphorus is missing.

• Nitrogen, Iron, Phosphorus — iron is a MICRONUTRIENT (needed only in trace amounts); potassium is missing.

• Potassium, Calcium, Sulphur — both calcium and sulphur are SECONDARY nutrients, and nitrogen and phosphorus are both missing.

Cross-check

Fertiliser grades are universally labelled by their N-P-K ratio (for example 10-26-26), confirming that Nitrogen, Phosphorus and Potassium are the three primary nutrients a fertile soil must carry, alongside the trace micronutrients.