Which of the following statements are true?
$(A)$ The subsidiary quantum number $\ell$ describes the shape of the orbital occupied by the electron.
$(B)$ The image shows the boundary surface diagram of the $2p_x$ orbital.
$(C)$ The $+$ and $-$ signs in the wave function of the $2p_x$ orbital refer to charge.
$(D)$ The wave function of the $2p_x$ orbital is zero everywhere in the $yz$ plane.

Which of the following statements are correct?
$(A)$ The electronic configuration of $Cr$ is $[Ar] 3d^5 4s^1$.
$(B)$ The magnetic quantum number may have a negative value.
$(C)$ In the ground state of an atom, the orbitals are filled in order of their increasing energies.
$(D)$ The total number of nodes is given by $n-1$.
Choose the most appropriate answer from the options given below.

The plot of $r^2 \Psi^2$ versus $r$ for $2s$ orbital of hydrogen atom exhibits :-

The hydrogen-like species $Li^{2+}$ is in a spherically symmetric state $S_1$ with one radial node. Upon absorbing light,the ion undergoes transition to a state $S_2$. The state $S_2$ has one radial node and its energy is equal to the ground state energy of the hydrogen atom.
$1.$ The state $S_1$ is
$(A)$ $1s$ $(B)$ $2s$ $(C)$ $2p$ $(D)$ $3s$
$2.$ Energy of the state $S_1$ in units of the hydrogen atom ground state energy is
$(A)$ $0.75$ $(B)$ $1.50$ $(C)$ $2.25$ $(D)$ $4.50$
$3.$ The orbital angular momentum quantum number of the state $S_2$ is
$(A)$ $0$ $(B)$ $1$ $(C)$ $2$ $(D)$ $3$
Give the answer for questions $1, 2$ and $3.$

The maximum number of electrons that can be accommodated in a $3d$ subshell is

What are the values of $n$ and $l$ for the $f$-subshell with the lowest energy?