Rutherford's $\alpha$-particle scattering experiment established the existence of
Aa small, dense, positively-charged nucleus
Belectrons spread uniformly across the atom
Cneutrons inside the nucleus
Ddiscrete energy levels
Answer & Solution
Correct answer: A. a small, dense, positively-charged nucleus
The unexpected back-scattering of a few alpha particles ruled out Thomson's plum-pudding model. Only a tiny positively-charged region — too small to scatter most $\alpha$'s but heavy and charged enough to deflect a few by large angles — could explain the result. That region is the nucleus.
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