The correct answer is (a) Balmer.
The Balmer series is a series of spectral lines in the visible and ultraviolet regions of the electromagnetic spectrum produced by the hydrogen atom when an electron transitions from an outer shell to the second shell. The series is named after Johann Balmer, who discovered it in 1885.
The Lyman series is a series of spectral lines in the ultraviolet region of the electromagnetic spectrum produced by the hydrogen atom when an electron transitions from an outer shell to the first shell. The series is named after Theodore Lyman, who discovered it in 1914.
The Paschen series is a series of spectral lines in the infrared region of the electromagnetic spectrum produced by the hydrogen atom when an electron transitions from an outer shell to the third shell. The series is named after Friedrich Paschen, who discovered it in 1908.
The Pfund series is a series of spectral lines in the infrared region of the electromagnetic spectrum produced by the hydrogen atom when an electron transitions from an outer shell to the fourth shell. The series is named after August Pfund, who discovered it in 1921.
The Balmer series is the only one of these series that is found in the visible region of the electromagnetic spectrum.