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

The configuration $1s^2 2s^2 2p^5 3s^1$ shows:

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 number of electrons that can be accommodated in $d_{z^2}$ orbital is

What will be the maximum number of electrons in any atom having quantum numbers $n = 4, l = 2, m = -2$?

Identify the element if its expected electronic configuration is $[Ar] 3d^{10} 4s^{2}$.