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

$A$ farmer adds/supplies $Na, Ca, Mg$ and $Fe$ regularly to his field and yet he observes that the plants show deficiency of $Ca, Mg$ and $Fe$. Give a valid reason and suggest a way to help the farmer improve the growth of plants.

Identify the mismatched pair.

Which mineral element is essential regarding respiratory pigments in invertebrates and vertebrates?

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

Nitrates of soil are also leached deep into the earth by . . . . . . .