Not considering the electronic spin,the degeneracy of the second excited state $(n=3)$ of $H$ atom is $9$,while the degeneracy of the second excited state of $H^{-}$ is

The number of radial nodes in a $2s$ orbital is equal to that in a ........ orbital.

Arrange the orbitals of $H$-atom in the increasing order of their energy:
$3p_x, 2s, 4d_{xy}, 3s, 4p_z, 3p_y, 4s$

For a hydrogen atom,the orbital$(s)$ with the lowest energy is/are:
$A$. $4s$
$B$. $3p_x$
$C$. $3d_{x^2-y^2}$
$D$. $3d_{z^2}$
$E$. $4p_z$
Choose the correct answer from the options given below:

An atom with atomic number $15$ contains:

Which of the following statement$(s)$ is/are true?
$A$. If two orbitals have the same value of $(n+l)$, the orbital with lower value of $n$ will have lower energy.
$B$. Energies of the orbitals in the same subshell increase with increase in atomic number.
$C$. The size of $2p_x$ orbital is less than the size of $3p_x$ orbital.
$D$. Among $5f, 6s, 4d, 5p$ and $5d$ orbitals, none of the orbitals have $2$ radial nodes.