Which of the following statements is true regarding the hydrogen atom?

Identify the orbital having the lowest energy from the following.

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

Given below are two statements. One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$ : Energy of $2s$ orbital of hydrogen atom is greater than that of $2s$ orbital of lithium.
Reason $R$ : Energies of the orbitals in the same subshell decrease with increase in the atomic number.
In the light of the above statements,choose the correct answer from the options given below.

The sum of electrons present in all subshells of an atom with $m_s$ value of $+\frac{1}{2}$ for $n=4$ and $m_s$ value of $-\frac{1}{2}$ for $n=3$ is

Which quantum number determines the shape of the subshell?