For the last electron entering the electronic configuration of potassium $(K)$,the values of $n, l,$ and $m$ are respectively .......

Given below are two statements. One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$ : Energy of $2s$ orbital of hydrogen atom is greater than that of $2s$ orbital of lithium.
Reason $R$ : Energies of the orbitals in the same subshell decrease with increase in the atomic number.
In the light of the above statements,choose the correct answer from the options given below.

What is the total number of orbitals present in $N$ shell?

What does magnetic quantum number describe?

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 correct order of energy of $2s$-orbitals in $H$,$Li$,$Na$ and $K$ is: