Directions: Read the Assertion (A) and Reason (R) carefully and choose the correct alternative. Assertion (A): Leguminous plants help to revive and improve soil fertility. Reason (R): Microorganisms present in the root nodules of leguminous plants fix atmospheric nitrogen into usable forms in the soil.

Introduction / Context:
This Assertion and Reason question examines basic concepts of soil fertility and the role of leguminous plants in agriculture. It focuses on biological nitrogen fixation, a key idea in biology and environmental science. Farmers often include legumes such as peas, beans, and pulses in crop rotation to improve soil fertility, and this question asks you to connect that practice with the activity of microorganisms in the root nodules.

Given Data / Assumptions:

• Leguminous plants are those that belong to the pea family, such as gram, peas, beans, and lentils.
• Assertion (A) states that legumes revive soil fertility.
• Reason (R) states that microbes in root nodules of legumes fix atmospheric nitrogen.
• We assume the standard school level explanation of nitrogen fixation in biology and agriculture.

Concept / Approach:
Nitrogen is an essential nutrient for plants but cannot be directly used by most plants in its gaseous form as N2. Certain bacteria can convert atmospheric nitrogen into nitrogenous compounds like nitrates and ammonium that plants can absorb through their roots. In leguminous plants, some of these nitrogen fixing bacteria, for example Rhizobium species, live in root nodules in a symbiotic relationship. This biological nitrogen fixation naturally enriches the soil with nitrogen compounds, improving fertility without chemical fertilisers.

Step-by-Step Solution:
Step 1: Consider Assertion (A). In practice, farmers often grow legumes in crop rotation, and scientific studies show that legumes can improve nitrogen content in soil. Therefore Assertion (A) is true. Step 2: Reason (R) states that microbes in root nodules of legumes fix atmospheric nitrogen. This is a well known fact. Bacteria like Rhizobium infect legume roots, form nodules, and convert nitrogen gas into compounds that the plant can use. Step 3: These nitrogenous compounds not only nourish the legume plant but also remain in the soil as part of organic matter or as leftover nitrates, thereby enriching the soil for subsequent crops. Step 4: Because of this biological nitrogen fixation, the soil where legumes have grown becomes more fertile compared to fields without such crops, especially in terms of nitrogen availability. Step 5: Therefore Reason (R) is true and provides the direct scientific explanation for why Assertion (A) is correct.

Verification / Alternative check:
Agriculture and biology textbooks repeatedly highlight crop rotation with legumes as an eco friendly way to maintain or improve soil fertility. They show diagrams of legume roots with nodules and explain how nitrogen fixing bacteria live there. These explanations explicitly connect the presence of root nodules and nitrogen fixation with improved soil fertility. This independent confirmation supports both the truth of Assertion (A) and the explanatory role of Reason (R).

Why Other Options Are Wrong:
Options that state that Assertion (A) is false contradict well established agricultural practice. Options that deny the truth of Reason (R) conflict with standard microbiology facts. The option claiming both are true but R does not explain A is also incorrect because nitrogen fixation is exactly the reason legumes enrich the soil.

Common Pitfalls:
A typical mistake is to think that only chemical fertilisers can improve soil fertility and to ignore natural processes like symbiotic nitrogen fixation. Another pitfall is confusing nitrogen fixation by bacteria with nitrogen absorption by plant roots. In this question, the microorganisms in root nodules are the key players that convert atmospheric nitrogen into plant usable forms.

Final Answer:
Both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A), so the correct option is Both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A).