The series of hydrogen spectrum which lies in the visible region is:

The correct answer is Option (3) → Balmer series

In the hydrogen spectrum each series is formed by transitions ending on one lower level \( n_1 \); the larger the energy gap, the shorter the wavelength.

Option (1) Paschen series — Incorrect. The Paschen series ends on \( n = 3 \); its energy gaps are small and it lies in the infrared.

Option (2) Lyman series — Incorrect. The Lyman series ends on \( n = 1 \); its photons have the largest energies and lie in the ultraviolet.

Option (3) Balmer series — Correct. The Balmer series ends on \( n = 2 \); its first lines, from 656 nm down to about 410 nm, lie in the visible region.

Option (4) Brackett series — Incorrect. The Brackett series ends on \( n = 4 \) and lies far in the infrared.

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 – “… Each of these sets is called a 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).”