Calculate the radius of the first orbit of $He^{+}$. (in $pm$)

What is the radius of the fourth orbit of $Be^{3+}$ (in $pm$)?

$A$ $200 \ W$ bulb emits monochromatic light of wavelength $200 \ nm$. Calculate the number of photons emitted per second by the bulb.

The energy of an electron in the first Bohr orbit of $H$ atom is $-13.6 \ eV$. The possible energy value$(s)$ of the excited state$(s)$ for electrons in Bohr orbits of the hydrogen atom is(are) $............ \ eV$.

What is the relation between radius, order of orbit, and nuclear charge for hydrogen-like species?

The electron in a hydrogen atom,upon absorbing $12.75 \ eV$ of energy,will jump to the ....... orbit.