An orange emission line is observed at 656.3 nm in the hydrogen emission spectrum. Determine the initial energy level of the electron.

The energy of a wave is calculated by E = hf where f is the frequency and h is the Planck's constant (6.626 * 10^-34 J/s).

The formula may be written as E = hc/λ where c is the speed of light 3*10^8 m/s and λ is the wavelength.

Thus energy = (6.626 * 10^-34) * (3 * 10^8) / (656.3 nm)

= 3.0267 * 10^ - 19 J

Therefore, the initial energy level of an electron is 3.0267 * 10^-19 joules.