Assertion: Escherichia coli, Shigella sp and Salmonella sp are all responsible for diarrhoeal diseases.
Reason: Dehydration is common to all types of diarrhoeal diseases and adequate supply of fluids and electrolytes should be ensured.

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that Escherichia coli, Shigella sp, and Salmonella sp are all responsible for diarrheal diseases.
- **Explanation**: These bacteria are known pathogens that infect the gastrointestinal tract, leading to symptoms such as diarrhea. This part of the assertion is true.

2. **Understanding the Reason**: The reason provided is that dehydration is common to all types of diarrheal diseases and that an adequate supply of fluids and electrolytes should be ensured.
- **Explanation**: Diarrhea often leads to significant loss of fluids and electrolytes from the body, resulting in dehydration. This statement is also true.

3. **Evaluating the Relationship**: Now, we need to determine if the reason is the correct explanation for the assertion.
- **Analysis**: While both statements are true, the reason does not specifically explain why the bacteria mentioned in the assertion cause diarrheal diseases. The assertion focuses on the causative agents (the bacteria), while the reason discusses the consequences (dehydration) without linking it back to the specific role of the bacteria.

4. **Conclusion**: Since both the assertion and the reason are true, but the reason does not correctly explain the assertion, we conclude that:
- **Final Answer**: Both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.