Question

Assertion: Young leaves are first to show nitrogen deficiency.
Reason: There is normal pigment synthesis in nitrogen deficient conditions.
A. Both assertion and reason are correct and reason is the correct explanation for assertion.
B. Both assertion and reason are correct and reason is the correct explanation for assertion.
C. Assertion is correct but the reason is not correct.
D. Assertion is not correct but the reason is correct.

Answer 1

Nitrogen is an essential component of plant development. It may be present in good soils and provides energy to plants, allowing them to develop and produce fruit or vegetables. Nitrogen is a component of the chlorophyll molecule, which gives plants their green color and is involved in photosynthesis, which produces food for the plant. Nitrogen is also the essential component of proteins and nucleic acids.
Concept used:
In plants nitrogen is an essential element and if any plant grows in nitrogen deficient conditions then the nitrogen from its dead and senescent leaves mobilizes to young growing leaves to ensure proper growth of the plant. Furthermore, under nitrogen deficient conditions synthesis of various pigments associated with photosynthesis is affected which leads to a change in leaf coloration to reddish and purplish colors.

Complete solution:
Option: A and B – Based on the factual concepts about nitrogen deficiency in plants it becomes clear that assertion and the reason both are incorrect.
Thus, Option A and B are incorrect.
Option: C – This option is also not correct since not just the reason but the assertion is also wrong.
Thus, Option C is also not correct.
Option: D – This option is correct because both the assertion and reason are wrong. In the question the assertion says that young leaves are first to show nitrogen deficiency which is wrong because in nitrogen deficiency, the mobilization of nitrogen occurs from dead and senescent parts of the plant to the younger growing parts in order to ensure optimal growth of the plant.
Thus, Option D is the right answer.

Therefore, Option D) both the assertion and the reason are wrong, is the correct answer.

Note:
The following are some signs of nitrogen shortage (in the absence or insufficient supply):
The amount of chlorophyll in the plant leaves is decreased, resulting in a light-yellow hue (chlorosis). The older the leaves become, the more yellow they get.
The amount of flowering, fruiting, protein, and starch in the plant is lowered. Protein deficiency causes slowed development and inactive lateral buds.
The plant seems to be light and yellow in colour due to starvation.