Ammonia provided to crop plants in the form of urea is industrially fixed by . . . . . . .

Which one of the following is a wrong statement?

Which of the following plants are used as green manure in crop fields and in sandy soils?

Select the correct match for $X$ and $Y$:

Column $X$	Column $Y$
$(1)$ Mycorrhiza	$(P)$ Free-living $N_2$-fixer
$(2)$ Nostoc	$(Q)$ Phosphorus absorption
$(3)$ Azospirillum	$(R)$ Leguminous plants
$(4)$ Rhizobium	$(S)$ Autotrophic $N_2$-fixer

Which of the following statements are true? If false,correct them:
$(a)$ Boron deficiency leads to stout axis.
$(b)$ Every mineral element that is present in a cell is needed by the cell.
$(c)$ Nitrogen as a nutrient element,is highly immobile in the plants.
$(d)$ It is very easy to establish the essentiality of micronutrients because they are required only in trace quantities.

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 : ........