The most immobile nutrient in plants is…

✅Explanation: Both boron (B) and calcium (Ca) are considered relatively immobile nutrients in plants. This means that they are not easily transported from older tissues to younger growing tissues. Therefore, deficiencies of these nutrients often manifest in younger leaves and growing points.

📌 Other Options Explanations:
-(B) Mo (Molybdenum) and B (Boron): While boron is immobile, molybdenum is relatively mobile within the plant.
-(C) Mo (Molybdenum) and Zn (Zinc): While molybdenum is mobile, zinc is considered to have intermediate mobility in plants.
-(D) Cu (Copper) and Fe (Iron): Both copper and iron are considered immobile nutrients in plants.

🔑Key Points::
-An essential nutrient is one required by an organism for normal growth and development.
-An essential element cannot be manufactured on its own.
-There are 17 elements that are essential for plants.  
-Therefore, depending upon the number of nutrients present in plants, these elements are grouped into three categories: basic nutrient, macronutrient and micronutrient.

• Basic Nutrients:
– It forms about 95% of the dry weight of a plant.
-It comprises three elements namely, carbon, hydrogen, and oxygen.
-They are taken by the plant from the air and water.

• Macronutrients:
-Generally present in plant tissues in large amounts (in excess of 10 mole Kg –1 of dry matter). 
-The macronutrients include nitrogen (N), phosphorous (P), sulfur (S), potassium (K), calcium (Ca), and magnesium (Mg).
-Among these, N, P and K are called primary nutrients.
-Whereas Ca, Mg, and S are known as secondary nutrients.
-They are known as secondary nutrients due to their secondary importance to the manufacturer of primary nutrient fertilizers.

• Micronutrients:
-Micronutrients or trace elements are needed in very small amounts (less than 10-mole Kg –1 of dry matter).
-These include iron, manganese, copper, molybdenum, zinc, boron, chlorine, and nickel.

• Mobile nutrients:
-These nutrients are able to move out of older leaves to younger plant parts when supplies are inadequate.
-Mobile nutrients include N, P, K, chlorine (Cl), Mg, and molybdenum (Mo).
-Because these nutrients are mobile, visual deficiencies will first occur in the older or lower leaves.
-Its effects can be either localized or generalized.