What results do you expect if alpha-particle scattering experiment is
repeated using a thin sheet of hydrogen in place of a gold foil ?
Explain. (Hydrogen is a solid at temperature below 14K)

In the alpha-particle scattering experiment, if we use a thin sheet of solid hydrogen(  with temperature below 14 K) is used in place of a gold foil, then the scattering angle produced by the collision even by the head on collision would not be large.
As the mass of hydrogen is less than the mass of incident α−particles . Thus, even in a head-on collision, the alpha-particle will not be scattered back as i terms of mass, the scattering particle is more massive than the target nucleus (hydrogen).
The mass of hydrogen atom=1.67 × 10 ⁻²⁷ kg
Mass of gold atom =6.64 × 10 ⁻²⁷ kg
In conclusion, the α−particles would not bounce back if solid hydrogen is used in the α-particle scattering experiment.