The element used by Rutherford in his famous scattering experiment was

What is the ratio of the radius of the second Bohr orbit to the first Bohr orbit of the $H$ atom?

Which of the following statements is $NOT$ true about the $Bohr$ atomic model?

If the wave number of radiation emitted for the electron transition from an excited state to ground state of hydrogen is $\frac{5x}{36} \ m^{-1}$,the wave number of radiation absorbed for the electron transition from the above excited state to the next immediate excited state in $m^{-1}$ is:

The $\alpha$-particle scattering experiment of Rutherford concluded that

When electromagnetic radiation of wavelength $300 \, nm$ falls on the surface of sodium,electrons are emitted with a kinetic energy of $1.68 \times 10^{5} \, J \, mol^{-1}$. What is the minimum energy needed to remove an electron from sodium? What is the maximum wavelength that will cause a photoelectron to be emitted?