Explain in terms of both electrons and energy how the bright line spectrum of an element is produced

The atoms don't absorb the energy; the electrons absorb the energy. Electrons around atoms, without energy, are in an unexcited state, called a ground state. Once energy is absorbed, however, the electrons become excited, meaning they have more energy and are going to release it. Once they are excited, they make a transition from a lower valence shell to a higher valence shell, which is the transition state. Then, the electrons fall back to their own valence shell, releasing the energy, and are put in the ground state again. The energy that is released as quanta, which is how a bright-line spectrum is produced.

Gallium melts near room temperature and has one of the largest  liquid  ranges of any metal, so it has found use in high temperature thermometers.