Which orbital shell can hold a maximum of 18 electrons?

The third shell can hold a maximum of 18 electrons due to its sublevels' configurations. Each electron shell is composed of subshells (s, p, d, f), and the third shell includes the 3s, 3p, and 3d subshells.

To understand how the total of 18 electrons is derived, consider the following: The 3s subshell can hold 2 electrons, the 3p subshell can hold 6 electrons, and the 3d subshell can hold 10 electrons. When you add these together (2 + 6 + 10), you get a total of 18 electrons that the third shell can accommodate.

The other shells, such as the first, second, and fourth, have different maximum capacities. The first shell can hold a maximum of 2 electrons due to containing only the 1s subshell, while the second shell can hold 8 electrons (2 in 2s and 6 in 2p). The fourth shell can hold a maximum of 32 electrons, but it does not directly answer the query regarding the maximum for the third shell. Hence, the third shell uniquely fits the requirement of holding 18 electrons.