Final answer:
The principal quantum number, n, for the outermost electrons in a Br atom is 4.
Step-by-step explanation:
The principal quantum number, n, for the outermost electrons in a Br atom is 4.
The principal quantum number (n) is the main energy level occupied by the electron. It determines the average distance of an electron from the nucleus. As n increases, the average distance from the nucleus increases. Since Br has 35 electrons, the first four shells are filled with electrons, and the outermost shell, which is the fourth shell (n=4), contains the outermost electrons in a Br atom.