Determine the number of $d$-electrons in $Fe^{2+} (Z = 26)$.

What is the total number of orbitals associated with the principal quantum number $n = 3$?

If $n$ and $l$ are principal and azimuthal quantum numbers respectively,then the expression for calculating the total number of electrons in any energy level is:

Which of the following orbitals is non-directional?

The quantum numbers $n$ and $l$ for four electrons are given as: $(1) \, n = 4, l = 1; \, (2) \, n = 4, l = 0; \, (3) \, n = 3, l = 2; \, (4) \, n = 3, l = 1$. Arrange them in increasing order of their energy.

Which of the following sets of quantum numbers is not correct?