A spectroscope reveals a dark line at wavelength 247nm in the otherwise continuous spectrum of a gas sample. Which of the following best describes the atomic event that produces this type of spectral feature?
a) An electron in the gas emits a 247 nm photon and drops to a lower-energy state.
b) The nucleus of the atom absorbs a 247 nm photon, causing a nuclear transition.
c) An electron in the gas absorbs a 247 nm photon and moves to a higher-energy state.
d) An electron in the gas absorbs a 247 nm photon and drops to a lower-energy state.