Final answer:
An electron in the third energy shell has more potential energy because it is farther from the nucleus than an electron in the first energy shell. The increased distance reduces the nucleus's hold on the electron, increasing its potential energy.
Step-by-step explanation:
An electron in the third energy shell has more potential energy than an electron in the first energy shell. This is because electrons further away from the nucleus are less bound to the nucleus due to the increased distance. As the principal quantum number or shell number increases, the shells get further from the nucleus, which increases the potential energy of the electrons in those shells. The third energy shell is farther from the nucleus than the first, requiring energy to move an electron from the first to the third shell thus, an electron in the third shell possesses more potential energy.
When an electron absorbs energy, such as from a photon of light, it can move to a higher energy level, a process which is related to the electron's ability to move further from the nucleus into higher-energy shells (excited states). The process of an electron moving from a lower energy shell to a higher one involves an increase in both kinetic and potential energy, the latter being due to its higher position in the energy level framework of the atom.