If an atom has $13$ electrons in the $M$ shell and $1$ electron in the $N$ shell,then the number of unpaired electrons in that atom is ...

Which orbitals are present in a hydrogen atom?

Statement $1$: The energy of an electron is determined by the principal quantum number.
Statement $2$: The principal quantum number $(n)$ indicates the distance of the electron from the nucleus.

In a multi-electron atom,which of the following orbitals have the same energy in the absence of magnetic and electric fields? $(a) n = 1, l = 0, m = 0, (b) n = 3, l = 0, m = 0, (c) n = 2, l = 1, m = 1, (d) n = 3, l = 2, m = 1, (e) n = 3, l = 2, m = 0$

$(i)$ An atomic orbital has $n=3$. What are the possible values of $l$ and $m_l$?
$(ii)$ List the quantum numbers ($m_l$ and $l$) of electrons for $3d$ orbital.
$(iii)$ Which of the following orbitals are possible? $1p$,$2s$,$2p$,and $3f$.

An electron having the quantum numbers $n = 4, l = 3, m = 0, s = -\frac{1}{2}$ would be in the orbital