In a chromium atom,the number of electrons which have $n = 2$ and $l = 1$ is:

When the azimuthal quantum number has a value of $l = 0$,the shape of the orbital is

For the electronic configuration $1s^2 2s^2 2p^3$,what is the number of electrons having $n = 2, l = 1$,and $s = +1/2$?

Which electronic level would allow the hydrogen atom to absorb a photon but not to emit a photon?

Arrange the $1s$,$2s$,$4s$,$2p$,$3p$,$4p$,and $3d$ orbitals according to increasing order of energy.

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 $3.$