Electrons orbit the nucleus in discrete energy states or orbitals and can only transition between them by absorbing or releasing energy. Electrons cannot exist between orbitals.
Energy states are described using quantum numbers. The quantum number n is used to label each energy state, where the lowest energy state is the ground state at n=1.
The emission spectrum of a pure elemental sample will appear as spectral lines of discrete wavelengths, whereas a mixed sample will have an emission spectrum that is continuous over a range of wavelengths.
The Balmer series includes the transitions from higher energy states (n=3-7) down to the n=2 energy state.
The Balmer series spectral lines are in the visible region, with lines at 410.2 nm, 434.1 nm, 486.1 nm, and 656.3 nm.
Source: Smaa Koraym at Johns Hopkins University, MD, USA
Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.