(N/A) In Rutherford's $\alpha$-particle scattering experiment,the scattering of $\alpha$-particles depends on the nuclear charge and mass of the target atoms.
Heavy atoms like gold $(Au)$ or platinum $(Pt)$ have a high nuclear charge $(Z)$ and a large mass,which results in strong electrostatic repulsion and significant scattering of $\alpha$-particles,including those that bounce back.
If a thin foil of lighter atoms like aluminium $(Al)$ is used,the nucleus has a smaller charge and lower mass. Consequently,the electrostatic repulsion between the $\alpha$-particles and the nucleus is weaker. This leads to a decrease in the number of $\alpha$-particles that are deflected at large angles and a significant reduction in the number of $\alpha$-particles that bounce back.