Which of the following rules or principles states that "No two electrons in an atom can have the same set of four quantum numbers"?

For an electron with $n = 3$,there is only one radial node. The orbital angular momentum of the electron will be

The angular part of the wave function for an orbital is given by $\psi_{(\theta, \phi)} = \left( \frac{15}{4\pi} \right)^{1/2} \sin \theta \cos \theta \sin \phi$,where $\theta$ is the angle from the $z$-axis. The angular node$(s)$ are:

The electron density between $1s$ and $2s$ orbital is

The electronic configuration of the element with atomic number $27$ is:

Which orbital has two angular nodal planes?