Final answer:
An atom is electrically neutral because it has equal numbers of protons and electrons, whose charges offset each other. Protons are made of quarks with fractional charges, but collectively they have a whole positive charge that balances the whole negative charge of electrons.
Step-by-step explanation:
An atom has no overall electric charge because it contains an equal number of positively charged protons and negatively charged electrons. These subatomic particles balance each other out, resulting in a neutral charge for the atom. While electrons are fundamental particles with no substructure, protons are composed of point-like particles known as quarks, which carry fractional charges. However, the charges on electrons and protons are unitary, meaning they are whole integer charges (positive and negative respectively) that balance out in a neutral atom. An imbalance in the number of protons and electrons leads to the formation of an ion, which is an electrically charged atom.