GATE 2021 BT – Question 9
Statements: All bacteria are microorganisms. All pathogens are microorganisms. Conclusions: I. Some pathogens are bacteria. II. All pathogens are not bacteria. Which option is logically correct?
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Correct answer: (C) Either I or II is correct; (D) Neither I nor II is correct
Explanation
The official key accepts either C OR D. These are separate accepted answers, not one continuous interval.
Let B = bacteria, M = microorganisms and P = pathogens.
**Statements:** all B are M, and all P are M. Both sets lie inside M, but nothing is said about how B and P relate to each other. They might overlap, be completely separate, or even coincide.
- **Conclusion I, "Some pathogens are bacteria".** This needs the two sets to overlap. The statements do not say so. Not certain. ✗
- **Conclusion II, "All pathogens are not bacteria".** This needs the pathogens to lie outside the bacteria. The statements do not say so either. Not certain. ✗
Neither conclusion is forced by the two statements, so **neither I nor II** follows (option D, which is the answer in the key).
Official GATE 2021 answer key: https://gate2026.iitg.ac.in/doc/download/Answer_keys2021/bt_2021.pdf