GATE 2024 CY – Question 48
Physical Chemistry · Spectroscopy: Atomic spectroscopy; Russell-Saunders coupling; Term symbols and spectral details; origin of selection rules. Rotational, Vibrational, Electronic and Raman spectroscopy of diatomic and simple polyatomic molecules. Line broadening and line widths; simple properties of Gaussian and Lorentzian line shapes. Molecular spectroscopy: Absorbance, Beer- Lambert’s law, Einstein’s coefficient, Jablonski diagram. Relationship of transition moment integral with molar extinction coefficient and oscillator strength. Basic principles of Nuclear Magnetic Resonance: Gyromagnetic ratio; Chemical shift, nuclear coupling. · 2 marks · Multiple select
Among the following, the NMR active nucleus(nuclei) is (are)
- $^{12}\mathrm{C}$
- $^{19}\mathrm{F}$
- $^2\mathrm{H}$
- $^{16}\mathrm{O}$
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: (B) $^{19}\mathrm{F}$; (C) $^2\mathrm{H}$
Explanation
A nucleus is **NMR active** if it has a non-zero nuclear spin $I$. Nuclei with an even number of protons and an even number of neutrons have $I=0$.
- **$^{12}$C:** 6 protons, 6 neutrons (even, even), $I=0$. Inactive. ✗
- **$^{19}$F:** 9 protons, 10 neutrons, $I=\tfrac12$. Active. ✓
- **$^2$H (deuterium):** 1 proton, 1 neutron (odd, odd), $I=1$. Active. ✓
- **$^{16}$O:** 8 protons, 8 neutrons (even, even), $I=0$. Inactive. ✗
Answer **$^{19}$F and $^2$H** (B and C).