If the uncertainty in velocity is $\frac{1}{2 m} \sqrt{\frac{h}{\pi}}$, then the ratio of uncertainty in position and momentum is

The total number of spectral lines observed when electron returns from the 6th shell to the 2nd shell in hydrogen atom is

The orbital angular momentum of an electron in $d$-orbital is equal to

In hydrogen atom, the minimum energy required to excite an electron from 2nd orbit to the 3rd orbit is