The four lines observed in the visible emission spectrum of hydrogen tell us that: a. We could observe more lines if we had a stronger prism. b. The spectrum is continuous. c. Only certain energies are allowed for the electron in a hydrogen atom. d. The hydrogen molecules they came from have the formula H4. e. There are four electrons in an excited hydrogen atom.

c. Only certain energies are allowed for the electron in a hydrogen atom

Explanation:

Emission spectrum are produced when the excited electron in a atom release the energy in the form of photons to come to ground state. These photons are of different wavelengths depending on the excitation state of emitting electron or transition of electron. These electromagnetic radiation are observed through prism to produce the spectrum.

As the name indicates this spectrum is produced by emission of energy. Although the electron can be excited by different methods such as by heating but the key point is that electrons in hydrogen atom will emit the photons of same energy which they absorb and each electron can absorb only certain type of energy. So four lines were observed in the visible spectrum of hydrogen because only certain energies are observed for hydrogen atom.

it should be p1 v1 = p2 v2