The number of given orbitals which have electron density along the axis is $..........$. $p_{x}, p_{y}, p_{z}, d_{xy}, d_{yz}, d_{xz}, d_{z^2}, d_{x^2-y^2}$

$4s^2$ is the configuration of the outermost orbit of an element. Its atomic number would be $:-$

After filling the $4d$ orbitals,an electron will enter in:

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 $3.$

Which of the following orbitals does not have any directional properties?

The number of orbitals in the fourth principal quantum number $(n = 4)$ is: