Chuck wants to know how many electrons in an atom are not paired up. Which model would be best for Chuck to write out? - a set of quantum numbers for the last electron in the atom
- a configuration with numbers, letters, and superscripts
- a dot structure of the atom
- an orbital notation of the atom

an orbital notation of the atom

Explanation:

If Chuck wants to know how many electrons in an atom are not paired up, the model that would be best for Chuck to write out is an orbital notation of the atom.

Orbital notation is simply utilized to write the configuration of an electron so that certain information regarding the electrons that are contained in the atom of an element can be known. It should also be noted that the orbital notation can help in knowing an electron's quantum numbers.

Therefore, the answer is "an orbital notation of the atom".