Answer: Option B. -> a – 3, b – 4, c – 2, d – 1
:
B

Manganese is involved in the breaking down the water molecule during photosynthesis.
Diazotrophy is the ability to fix atmospheric nitrogen into a biologically useful form. This is done with the help of the nitrogenase enzyme, which requires an iron-molybdenum cofactor.
Cytochrome c oxidase contains a copper center consisting of 2 copper atoms.
Zinc is required for the synthesis of auxins. Indole 3 acetic acid (IAA) is a prominent auxin. 

Answer: Option A. -> The element is relatively immobile. 
:
A
Some deficiency symptoms tend to appear first in the young tissues whenever the elements are relatively immobile and are not transported out of the mature organs. Calcium is a part of the structural component of the cell and because of that it is not easily degraded and released for use by the younger growing regions of the plants. This causes the younger leaves to show the symptoms of the deficiency. 

Answer: Option B. -> Alcohol dehydrogenase
:
B
Alcohol dehydrogenase (ADH) have a structural zinc site. This $Z{n}^{2+}$ ion plays a structural role and is crucial for protein stability of the ADH enzyme.

Answer: Option B. -> False
:
B

Soil is a great reservoir for many minerals on this planet. Because of the mode of absorption of minerals in plants, most of the minerals in soil can enter the plants through their roots. Even though they might not have any role to play in the plant. Thus elements that have no role to play in plants have been found to be present in plants. 

Answer: Option B. -> Carbon
:
B

Carbon is the most abundant element found in plants. Plants use carbon dioxide during photosynthesis. They take in carbon dioxide and convert it to energy for growth. When the plant dies, carbon dioxide is given off from the decomposition of the plant.

Answer: Option D. -> Sulphur
:
D
Sulphur is a component of thiamine, biotin & CoA. Deficiency of sulphur in plants causes symptoms similar to the deficiency of nitrogen. 

Answer: Option B. -> A - Infection thread containing bacteria B - Inner cortical and pericycle cells under division
:
B
Rhizobia infects the root hair and forms infection thread. It causes inner cortical cells and pericycle cells to divide rapidly.

Answer: Option B. -> $N{O}_2,N{O}_3^{-}orN{H}_3$
:
B
In nitrogen fixation molecular nitrogen is converted into nitrogen oxides like $N{O}_2^{-}$, $N{O}_3^{-}$through physical nitrogen fixation process or ammonia through biological or chemical processes.

Answer: Option A. -> Both A & R are true and R explains A
:
A

Nitrogenase can only break N ≅ N bond and it is absent in higher plants, hence they cannot utilize $N_2$ present in the air.

Answer: Option B. -> Glutamic acid
:
B
From glutamic acid, more than 17 amino acids are formed through transamination which is the transfer of an amino group from one molecule to another, especially from an amino acid to a keto acid.