What is an energy sublevel?

An energy sublevel refers to a collection of atomic orbitals that share the same principal quantum number and have the same energy. In quantum mechanics, atomic orbitals are regions around the nucleus of an atom where electrons are likely to be found, and these orbitals can differ in shape and energy. Within a given principal energy level, such as n=1, n=2, etc., the orbitals can be grouped into sublevels that correspond to specific types of orbitals, like s, p, d, and f.

For instance, the first principal level (n=1) has only one sublevel (1s), while the second level (n=2) contains two sublevels (2s and 2p), both of which have the same principal quantum number but different shapes and orientations. This means that within a sublevel, all the orbitals will have the same energy, hence defining the sublevel. Therefore, the correct definition of an energy sublevel is a group of atomic orbitals that have the same energy, making option C the accurate choice.