Gold Foil Experiment Shows Atom's Mostly Empty Space

Steps:

• Most alpha particles pass undeflected, indicating atoms consist mostly of empty space.
• Rare deflections occur when alphas approach a central region closely.
• Large-angle scattering implies a tiny, massive, positively charged core repels alphas via Coulomb force.
• Thus, the nucleus must be very small to account for few interactions.

Why A is correct:

• The low deflection rate means the nucleus cross-section is ~10^-4 of the atom's, per Rutherford scattering formula, confirming its minuscule size.

Why the others are wrong:

• B: Deflections prove the nucleus is positively charged, repelling positive alphas.
• C: Passage through foil suggests empty space but doesn't specify electron arrangement.
• D: Electron charge was known from Thomson's work; experiment focuses on nuclear properties.

Final answer: A