An electron has a spin quantum number +1/2 and mag-netic quantum number −1. It cannot be present in:

The magnetic quantum number (ml) is derived from the azimuthal quantum number (l) and it can have values ranging from -l to +l, including zero. This means that the value of the magnetic quantum number is dependent on the value of the azimuthal quantum number.

Given that the electron has a magnetic quantum number (ml) of -1, the azimuthal quantum number (l) must be at least 1 (because l can be any non-negative integer: 0, 1, 2, 3,... and ml ranges from -l to +l).

Therefore, the electron cannot be present in an s orbital because for an s orbital, the azimuthal quantum number (l) is 0, and thus the magnetic quantum number (ml) can only be 0. So, an electron with a magnetic quantum number of -1 cannot be in an s orbital.