The ratio of the radii of hydrogen atom and its nucleus is ~ 105. Assuming the atom and the nucleus to be spherical,
(i) what will be the ratio of their sizes?
(ii) If atom is represented by planet earth ‘Re’ = 6.4 ×10 m, estimate the size of the nucleus.
(i) Volume of the sphere = 
Let R be the radius of the atom and r be that of the nucleus.
Volumes of nucleus = 
Nucleus of an atom is assumed to be a sphere.
Ratio of the size of atom to that of nucleus = 
⇒ R = 105 r
Hence, the radius of earth is equal to 105 the radius of the hydrogen atom.
(ii) If the atom is represented by the planet earth (R = 6.4×106m) then the radius of the nucleus would be equal to,
‘Re’= Radius of earth and ‘Rn’=radius of nucleus
Therefore, if the atom is represented by planet Earth, the size of its nucleus will be 64m.