Final answer:
The principal quantum number (n) indicates the shell of an atom, while the azimuthal quantum number (l) indicates the type of subshell. Different values of l correspond to different letters representing the subshells.
Step-by-step explanation:
The shell number in an atom is equal to the principal quantum number, denoted by n. The type of subshell corresponds to the azimuthal quantum number, denoted by l. The values of l determine the letter representation of the subshell.
For example, if l = 0, the subshell is called s; if l = 1, the subshell is called p; if l = 2, the subshell is called d; and if l = 3, the subshell is called f. These letters help distinguish the different subshells within a shell.
So, the principal quantum number indicates the shell (n) and the azimuthal quantum number indicates the subshell (l).