ANS:D - Sulphur

Among the options provided, Sulphur does not come under the category of 'primary nutrient' for plant growth. In plant nutrition, primary nutrients refer to the essential elements required by plants in relatively large quantities for their growth and development. These primary nutrients are nitrogen (N), phosphorus (P), and potassium (K). They play crucial roles in various physiological processes, such as photosynthesis, energy transfer, and enzyme activation. Sulphur, while essential for plant growth, is considered a secondary nutrient rather than a primary one. Secondary nutrients are required in smaller quantities compared to primary nutrients but are still essential for healthy plant growth. In addition to sulphur, secondary nutrients include calcium (Ca) and magnesium (Mg). Therefore, the correct answer is Sulphur. Nitrogen, phosphorus, and potassium are all primary nutrients necessary for plant growth.