Some positively charged alpha particles were deflected rather than passing straight through thin metal foil.To explain this,Rutherford postulated that the nucleus of the atom must be positive.

Question

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Rutherford's famous gold foil experiment led him to conclude that atoms have a small, dense, positively charged nucleus, since some of the positively charged alpha particles he shot at the foil were deflected or bounced back, indicating that they had encountered a positive charge.

Some Positively Charged Alpha Particles Were Deflected Rather Than Passing