Arrange the following series of emission lines in the spectrum of hyd…

The correct answer is Option (2) → (B), (C), (A)

Each series of the hydrogen spectrum is named by the lower level \( n_1 \) in which the electron lands: \( n_1 = 1 \) for Lyman, \( n_1 = 2 \) for Balmer and \( n_1 = 3 \) for Paschen. The wavelength follows from

    \( \displaystyle \frac{1}{\lambda} = R\left(\frac{1}{n_1^{2}} - \frac{1}{n_2^{2}}\right) \)

The lower the final level, the larger the energy released and the shorter the wavelength. The first (longest-wavelength) line of each series is

    \( \displaystyle \text{Lyman: } \frac{1}{\lambda} = \frac{3R}{4} \;\Rightarrow\; \lambda \approx 122\,\mathrm{nm} \)

    \( \displaystyle \text{Balmer: } \frac{1}{\lambda} = \frac{5R}{36} \;\Rightarrow\; \lambda \approx 656\,\mathrm{nm} \)

    \( \displaystyle \text{Paschen: } \frac{1}{\lambda} = \frac{7R}{144} \;\Rightarrow\; \lambda \approx 1875\,\mathrm{nm} \)

So the order of increasing wavelength is Lyman, Balmer, Paschen, that is (B), (C), (A).

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), but it is still in the CUET 2026 syllabus, so do not skip it.

NCERT (Pre-rationalised edition, 2022-23):
Spectral Series – “… In 1885, the first such series was observed by a Swedish school teacher Johann Jakob Balmer (1825–1898) in the visible region of the hydrogen spectrum. This series is called Balmer series (Fig. 12.6).”

Spectral Series – “… The Lyman series is in the ultraviolet, and the Paschen and Brackett series are in the infrared region.”