In any atom,which sub-shell will have the highest energy among the following?

The principal quantum number of an atom is related to the:

An element has an outermost orbital configuration of $4s^2$. What is its atomic number?

Consider the following statements :
$(a)$ Electron density in the $xy$ plane in $3d_{x^2-y^2}$ orbital is zero.
$(b)$ Electron density in the $xy$ plane in $3d_{z^2}$ orbital is zero.
$(c)$ $2s$ orbital has one nodal surface.
$(d)$ For $2p_z$ orbital,$yz$ is the nodal plane.
Select the incorrect statements $:-$

The sum of paired electrons present in $l = 2$ orbitals for the species $Fe^{2+}$,$Co^{2+}$,and $Ni^{2+}$ is .......

Which of the following pairs of orbitals possess two nodal planes?