Assertion : Biofertilisers are preferred to chemical fertilisers.
Reason : Chemical fertilisers are generally more expensive and hazardous to environment.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that biofertilizers are preferred to chemical fertilizers. This is a true statement. Biofertilizers are derived from natural sources, such as microorganisms, that enhance soil fertility and promote plant growth.

2. **Understanding the Reason**: The reason provided is that chemical fertilizers are generally more expensive and hazardous to the environment. This statement is also true. Chemical fertilizers can lead to environmental issues such as soil degradation, water pollution, and harm to beneficial soil organisms.

3. **Analyzing the Relationship**: The reason explains why biofertilizers are preferred over chemical fertilizers. The disadvantages of chemical fertilizers, including their cost and environmental impact, support the assertion that biofertilizers are a better choice.

4. **Conclusion**: Since both the assertion and the reason are true, and the reason correctly explains the assertion, we conclude that the correct answer is that both the assertion and reason are true, and the reason is a correct explanation of the assertion.

### Final Answer:
Both assertion and reason are true, and the reason is a correct explanation of the assertion.