GATE 2025 BM – Question 16
Assertion: PET uses radionuclides such as ¹¹C and ¹⁵N to study tissue metabolism. Reason: Positron-emitting nuclides are incorporated into molecules essential for metabolism. Choose the published assertion–reason classification.
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Correct answer: (B) Both true; reason explains assertion
Explanation
The published answer is B: PET follows metabolism by attaching positron-emitting isotopes to suitable tracer molecules, whose distribution is measured through annihilation photons. However, the source explicitly prints ¹⁵N, which is stable and is not a PET positron emitter; ¹³N or ¹⁵O are common relevant radionuclides. This isotope typo is retained and flagged rather than silently corrected. B is the official grading, not an endorsement of the printed isotope example.