Principal quantum number $\left(\mathrm{n}\right)$ : (Proposed by Bohr)
It describes the size of the electron wave and the total energy of the electron. It has integral values$1, 2, 3, 4....,$etc., and is denoted by $\mathrm{K}, \mathrm{L}, \mathrm{M}, \mathrm{N}. ....$

Azimuthal quantum number $\left(\mathrm{l}\right)$:-

It describes the shape of electron cloud and number of subshell in a shell.

So, for $\mathrm{n}=3, \mathrm{l}=2$, this represents the $3\mathrm{d}$ subshell. It can have the maximum ten electrons.

Hence, a subshell $\mathrm{n}=3, \mathrm{l}=2$ can accommodate maximum of $10 \mathrm{electrons}$.