The relation between $n_m$ ($n_m=$ the number of permissible values of magnetic quantum number ($m$)) for a given value of azimuthal quantum number ($l$), is:

1. A
   $l=\frac{n_m-1}{2}$
2. B
   $l=2n_m+1$
3. C
   $n_m=2l^2+1$
4. D
   $n_m=2l$