hydrogen has only one electron why does its spectrum have 4 colored lines

The spectral lines of hydrogen are not solely determined by the number of electrons. Instead, they arise from transitions between different energy levels of the electron within the atom.

In the case of hydrogen, when the electron absorbs energy, it can move from a lower energy level (closer to the nucleus) to a higher energy level (farther away from the nucleus). Conversely, when the electron loses energy, it moves from a higher energy level to a lower energy level. These transitions are accompanied by the emission or absorption of photons, which have specific energies corresponding to the energy difference between the levels involved.

The energy levels in hydrogen are quantized, meaning they have specific discrete values. The energy levels are represented by quantum numbers, with the lowest energy level called the ground state (n=1). As the energy level increases, the value of the quantum number (n) also increases.

The different colored lines in the hydrogen spectrum correspond to different energy transitions between these quantized energy levels. Four prominent spectral lines are observed in the visible region, known as the Balmer series, which are transitions involving the second energy level (n=2). These lines are red (n=3 to n=2), blue-green (n=4 to n=2), blue-violet (n=5 to n=2), and violet (n=6 to n=2).

Other series of spectral lines exist for hydrogen, such as the Lyman series in the ultraviolet region (involving transitions to the first energy level, n=1) and the Paschen series in the infrared region (involving transitions to the third energy level, n=3), among others.

So, although hydrogen has only one electron, its spectrum exhibits multiple colored lines due to the various energy transitions that can occur between different energy levels of the electron