The approximate ratio of the speed of light in vacuum to that of an electron in the first Bohr orbit of hydrogen atom is

If the radius and energy of the second Bohr orbit of hydrogen atom is $r_2$ and $E_2$. respectively. The radius and energy of the third Bohr orbit will be $\_\_\_\_$ respectively.

When a radiation of 300 nm is shined on five metals, namely $\mathrm{Li}, \mathrm{Mg}, \mathrm{Ag}, \mathrm{Cu}$ and K , the number of metals that show photoelectric effect are

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