12.2 Suppose you are given a chance to repeat the alpha-particle scattering experiment using a thin sheet of solid hydrogen in place of the gold foil. (Hydrogen is a solid at temperatures below 14 K.) What results do you expect?

Hint: The mass of the Hydrogen atom is less than the mass of the $\alpha$-particle.

Step 1: Compare the mass of the Hydrogen atom with the mass of the $\alpha$-particle.
The mass of hydrogen  is less than the mass of incident $\alpha$-particles . Thus, the mass of the scattering particle is more than the target nucleus (hydrogen).

Step 2: Analyse the scattering angle in this case.
In the alpha-particle scattering experiment, if a thin sheet of solid hydrogen is used in place of a gold foil, then the scattering angle would not be large enough and the $\alpha$-particles would not bounce back if solid hydrogen is used in the particle scattering experiment.