What is the atomic number of gold ? 

Ratio of longest wavelengths corresponding to Lyman and Balmer series in hydrogen spectrum is

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

Rutherford’s $\alpha$-particle experiment showed that the atoms have

If the force between the electron in the first Bohr orbit and the nucleus (proton) in hydrogen atom is $F$, then the force between them when the electron is in the second orbit is

What radioactive source did the Geiger and Marsden use in the scattering experiment?