The orbital occupied by an electron with quantum numbers $n = 4, l = 3, m = 0$ and $s = -\frac{1}{2}$ is called

In a multi-electron atom,which of the following orbitals described by the three quantum numbers will have the same energy in the absence of magnetic and electric fields?
$1. n = 1, l = 0, m = 0$
$2. n = 2, l = 0, m = 0$
$3. n = 2, l = 1, m = 1$
$4. n = 3, l = 2, m = 0$
$5. n = 3, l = 2, m = 0$

The number of unpaired electrons in $Fe^{3+}$ $(Z = 26)$ is:

The orbital angular momentum of an electron in an orbital is given by $\sqrt{l(l + 1)} \cdot \frac{h}{2\pi}$. For an $s$-electron,this momentum is:

Which of the following sets of quantum numbers is allowed?

What is a shell in the context of atomic structure?