The angular momentum of an electron moving in an orbit of hydrogen atom is $$\mathrm{1.5\left(\frac{h}{\pi}\right)}$$. The energy in the same orbit is nearly.

The half life of a radioactive substance is 20 minutes. In how much time, the activity of substance drops to $$\left(\frac{1}{16}\right)^{\text {th }}$$ of its initial value?

In hydrogen spectrum, the shortest wavelength in the Balmer series is $$\lambda$$. The shortest wavelength in the Bracket series is :

The radius of inner most orbit of hydrogen atom is $$5.3 \times 10^{-11} \mathrm{~m}$$. What is the radius of third allowed orbit of hydrogen atom?