Final answer:
The negative pion, also known as a pi-minus (π-), is composed of a down quark and an up antiquark, resulting in its negative charge.
Step-by-step explanation:
The quark structure of a negative pion (π-) consists of a down quark (d) and an up antiquark (Ū). A pion is a type of meson, which means it is a subatomic particle made up of a quark and an antiquark. Since it is a negative pion, its overall charge is negative. The down quark carries a charge of -1/3, while the up antiquark carries an equivalent positive charge of +2/3; this results in a total charge of -1 for the pion. Pions are involved in mediating the strong nuclear force that holds the atomic nucleus together, and they are examples of mesons—particles that contain a quark-antiquark pair.