The three primary soil micro- nutrients are

Essential plant nutrients are categorized based on the quantity required for growth. Macronutrients are needed in large amounts, while micronutrients (or trace elements) are required in tiny quantities [3]. The primary macronutrients are nitrogen (N), phosphorus (P), and potassium (K), which are the major building blocks of fertilizers [4]. Secondary macronutrients include calcium, magnesium, and sulfur [4]. Micronutrients include iron, zinc, manganese, copper, boron, molybdenum, chlorine, and nickel [2]. Although the question uses the term 'micro-nutrients' for nitrogen, phosphorus, and potassium, these are universally classified as the 'primary' nutrients in soil science and fertilizer management [4]. Options 1 and 2 include non-mineral or toxic elements like cadmium, while option 4 mixes micronutrients (boron, zinc) with a secondary macronutrient (magnesium) [4].

Sources

1. [2] Indian Economy, Nitin Singhania .(ed 2nd 2021-22) > Chapter 9: Agriculture > FERTILISERS > p. 302
2. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > 3) Agricultural sources: > p. 74
3. [4] https://en.wikipedia.org/wiki/Plant_nutrition
4. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > z. Micronutrientsl > p. 363