Thicker foil boosts scattering centers for more large-angle deflections

Steps:

• Large-angle deflections result from close Coulomb interactions with atomic nuclei.
• Probability of such deflections scales with the number of nuclei encountered.
• Doubling foil thickness doubles the nuclei per unit area along particle paths.
• This directly increases the fraction of particles experiencing large-angle scattering.

Why B is correct:

• Per Rutherford's scattering formula, cross-section for large-angle deflection is proportional to atomic density; double thickness doubles effective density and thus deflection proportion.

Why the others are wrong:

• A: Greater kinetic energy reduces deflection angles by decreasing Coulomb interaction time, lowering large-angle proportion.
• C: Fewer protons weaken the nuclear charge, reducing repulsive force and large-angle deflection probability.
• D: Higher emission rate increases total particles but not the per-particle deflection probability, so proportion stays unchanged.

Final answer: B