With the principle quantum number being 2, the maximum number that can share this is 8. You can use the general formula 2n^2 to calculate this number (n=quantum level), or you can use the concept of quantum numbers (n, l, m, s) to justify this answer.
Mechanical energy of a body is simply the combination of its kinetic energy and potential energy
In comparison see it is very easy in goolge
The Energy of an atom that emits a photon of wavelength 2.21 m is
3.028 × 10⁻¹⁹ J.I attached the working and the answer to the question below. I hope I was able to help.
Please note that C = speed of light, ν = frequency, λ= wavelength, h = Planck's Constant