Question

Critical elements for the plant growth are
(a) Na, K, and Ca
(b) Na, P, and Mg
(c) N, P, and K
(d) Mn, B, and Mo

Answer 1

Hint: Along with sunlight, water, and air, a plant also needs some nutrients for its growth and reproduction. These are termed as ‘essential elements’. There are 17 essential elements which can be classified based on their quantitative requirements in a plant.

Complete answer:
Essential elements are grouped into macronutrients and micronutrients. Macronutrients are required in large quantities i.e. more than 10 mmol/kg of dry matter. These include carbon, oxygen, hydrogen, nitrogen, potassium, phosphorus, sulfur, calcium, and magnesium.
Micronutrients or trace elements are required in very small amounts i.e lower than 10 mmol/kg of dry matter. These are iron, manganese, copper, molybdenum, zinc, boron, chlorine, and nickel.
Nitrogen, Phosphorus, and potassium of macronutrients are considered as the critical element trinity by farmers and agriculturists alike. This is due to their immense requirement in the field, the absence of which is the primary cause of stunted growth in the crops. These are the three big nutrients that are available in almost all chemical fertilizers available in the market in varying concentrations.
- Nitrogen is obtained from the soil in the form of nitrates, nitrite, and ammonium salts. It is a constituent of amino acids, some coenzymes, and chlorophyll.
- Phosphorus is obtained from the soil in the form of phosphates like dihydrogen phosphate or hydrogen phosphate. It is a component of nucleic acids, phospholipids, chemical energy such as ATP, NADP.
- Potassium is absorbed in the form of potassium ions. It is required for the metabolic activities of cells in young growing parts like root tips and young leaves.
So, the correct answer is ‘N, P, and K.’

Note:
-The deficiency of nitrogen causes loss of chlorophyll or chlorosis which begins from older leaves and progresses to younger leaves.
-The deficiency of phosphorus causes premature leaf fall, stunted growth, and dormancy of lateral buds.
-The deficiency of potassium causes necrosis or death of plant tissues and loss of apical dominance which leads to bushy growth.