The diagram shows the path of four $\alpha  - $ particles of the same energy being scattered by the nucleus of an atom simultaneously. Which of these are/is not physically possible

If in nature there may not be an element for which the principal quantum number $n > 4,$ then the total possible number of elements will be

The diagram below shows the lowest four energy levels for an electron in a hypothetical atom.The electron is excited to the $-1\,eV$ level of the atom and transitions to the lowest energy state by emitting only two photons. Which of the following energies could not belong to either of the photons ? .....$eV$

Explain Rutherford's argument for scattered $\alpha $ -particles. 

In an atom, two electrons move around the nucleus in circular orbits of radii $R$ and $4R.$ The ratio of the time taken by them to complete one revolution is : (neglect electric interaction)

Explain the formulas of energy of electron in atom revolving around the nucleus in different orbits.