The wavelengths involved in the spectrum of deuterium (₁²D) are slightly different from that of hydrogen spectrum, because (a) the size of the two nuclei are different (b) the nuclear forces are different in the two cases (c) the masses of the two nuclei are different (d) the attraction between the electron and the nucleus is different in the two cases

Answer: (c). Rydberg constant depends on the reduced mass μ = (me M)/(me + M) of electron and nucleus. Deuterium nucleus is about twice as heavy as the proton, so μ and hence R change slightly. Charge (attraction) is the same; nuclear size and nuclear forces do not affect the levels. So the answer is (c).

The wavelengths involved in the spectrum of deuterium (₁²D) are… | JEE Main 2003 (AIEEE)

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Transitions, Photon Emission & Excitation

The wavelengths involved in the spectrum of deuterium $\left({}_{1}^{2}D\right)$ are slightly different from that of hydrogen spectrum, because

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Answer: (c)

Rydberg constant depends on the reduced mass $\mu = \frac{m_e M}{m_e + M}$ of electron and nucleus.
Deuterium nucleus is about twice as heavy as the proton, so $\mu$ and hence $R$ change slightly.
Charge (attraction) is the same; nuclear size and nuclear forces do not affect the levels.
So the answer is (c).

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