According to the Bohr model for the hydrogen atom,the radius of stationary orbits is proportional to which of the following?

Calculate the energy associated with the first orbit of $He^{+}$. What is the radius of this orbit?

Calculate the wavelength for the emission transition if it starts from the orbit having radius $1.3225 \, nm$ and ends at $211.6 \, pm$. Name the series to which this transition belongs and the region of the spectrum.

When the frequency of light incident on a metallic plate is doubled,the $KE$ of the emitted photoelectrons will be:

Electrons with a kinetic energy of $6.023 \times 10^4 \ J/mol$ are evolved from the surface of a metal when it is exposed to radiation of wavelength $600 \ nm$. The minimum amount of energy required to remove an electron from the metal atom is

In Rutherford's experiment,generally the thin foil of heavy atoms,like gold,platinum etc. have been used to be bombarded by the $\alpha$-particles. If the thin foil of light atoms like Aluminium etc. is used,what difference would be observed from the above results?