What is the approximate angular momentum (in J s ) of electron in hydrogen atom in its ground state?

$$ \left(h=6.625 \times 10^{-34} \mathrm{~J} \mathrm{~s}\right) $$

The energy of electron in hydrogen atom when present in $n=1, n=2$ and $n=3$ will be in the ratio of

The radius of first Bohr orbit of hydrogen atom is same as that of orbit $(n)$ of hydrogen like species $X .(n)$ and $X$ respectively are

Identify the impossible quantum number set for the electron from the following.