GATE 2021 BT – Question 48

Recombinant DNA Technology and Other Tools in Biotechnology · Analytical tools: Microscopy and spectroscopy · 2 marks · Multiple select

Which nuclei are NMR active?

$^1H$
$^{13}C$
$^{16}O$
$^{32}S$

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Correct answer: (A) $^1H$; (B) $^{13}C$

Explanation

A nucleus is **NMR active** if it has a non-zero nuclear spin. Spin depends on the numbers of protons and neutrons: nuclei with an odd number of protons or neutrons (odd mass number, or odd-odd) have spin, while nuclei with even numbers of both have zero spin.

**¹H:** 1 proton, spin ½. Active. ✓
**¹³C:** 6 protons and 7 neutrons (odd), spin ½. Active. ✓
**¹⁶O:** 8 protons and 8 neutrons (even, even), spin 0. Inactive. ✗
**³²S:** 16 protons and 16 neutrons (even, even), spin 0. Inactive. ✗

Answer **¹H and ¹³C** (A and B).