Which of the following series spectrum of hydrogen atom lies in ultraviolet region?

The wavelength $\lambda$ of the spectral lines in the hydrogen atom is given by the Rydberg formula: $\dfrac{1}{\lambda} = R \left( \dfrac{1}{n_1^2} - \dfrac{1}{n_2^2} \right)$, where $n_1$ is the lower energy level and $n_2$ is the higher energy level.

For the Lyman series, $n_1 = 1$ and $n_2 = 2, 3, 4, \dots$. The transitions to the ground state ($n_1 = 1$) involve large energy differences, which correspond to the ultraviolet region of the electromagnetic spectrum.

For the Balmer series, $n_1 = 2$, which lies in the visible region.

For the Paschen series, $n_1 = 3$, which lies in the infrared region.

For the Brackett series, $n_1 = 4$, which lies in the infrared region.

For the Pfund series, $n_1 = 5$, which lies in the infrared region.

Therefore, the Lyman series is the only one among the given options that lies in the ultraviolet region.

Answer: Lyman series