Plants require different minerals because......

Analogy type questions:
$(1)$ Manganese toxicity : Brown spots surrounded by chlorotic veins : Molybdenum deficiency : ........
$(2)$ Conversion of nitrogen to ammonia : Nitrogen fixation : Oxidation of nitrite to nitrate : ........

Consider the following statements regarding mineral nutrition:
$(a)$ Moderate decrease or increase of micronutrients causes deficiency and toxicity symptoms respectively.
$(b)$ Excess of manganese causes toxicity of iron, calcium and molybdenum.
$(c)$ $A$ macronutrient is said to be toxic when present below a critical concentration.
Which of the above statements are correct?

Which of the following organisms does not fix $N_2$?

Identify the $INCORRECT$ statement regarding the role of minerals in plants.

Which one of the following is a wrong statement?