The soil organisms are

$A$: Plants absorb nitrogen from the soil in the form of salts.
$R$: Nitrogen is essential for the synthesis of proteins and nucleic acids.

Nitrogen is required mainly by which of the following parts of the plants?
$I.$ Meristematic tissues
$II.$ Differentiating tissues
$III.$ Apical tissues
$IV.$ Metabolically active cells
Choose the correct option.

Match the columns:
$I$ $II$
$(A)$ Magnesium $(i)$ Found in middle lamella
$(B)$ Sulphur $(ii)$ $A$ structural component of chlorophyll
$(C)$ Calcium $(iii)$ Required for enzyme activity
$(D)$ Iodine $(iv)$ Found in some amino acids
$(E)$ Manganese $(v)$ $A$ component of sugars
$(vi)$ Not important for plants

Which of the following is considered to be the best chemical method of fixing atmospheric nitrogen?

Assertion $A$: Leguminous plants increase soil fertility.
Reason $R$: Azotobacter fixes atmospheric $N_2$.