Final answer:
The number of electrons in an atom that can be described by the quantum number n=2 is 8.
Step-by-step explanation:
The quantum number n=2 describes the second energy level or shell in an atom. Within this shell, there are two subshells: 2s and 2p. The 2s subshell can hold a maximum of 2 electrons, while the 2p subshell can hold a maximum of 6 electrons. Therefore, the total number of electrons that can be described by the quantum number n=2 is 2+6=8.