Compare an electrically neutral atom of oxygen and an isotope of oxygen.

An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive charge if there are fewer electrons (electron deficiency) or negative charge if there are more electrons (electron excess).

True, the standard unit for volume is liters which can be represented by either a lower case "l" or a capital "l"

In any atom of any element, you will find protons and neutrons in the nucleus of any atom