Question

question 8 of 10
what did rutherford observe that surprised him?

a. all of the alpha particles shot at the gold foil bounced back.

b. some of the alpha particles shot at the gold foil bounced back.

c. none of the alpha particles went through the gold foil.

d. all of the alpha particles went straight through the gold foil.

Explanation:

In Rutherford's gold foil experiment, the prevailing model at the time suggested atoms were mostly positive charge spread out (plum pudding model). So, when alpha particles (positively charged) were shot at gold foil, the expectation was they would mostly pass through with minor deflections. However, Rutherford observed that while most alpha particles did pass through, some (a small fraction) bounced back (were deflected at large angles), which was surprising as it contradicted the existing model and implied a dense, positively - charged nucleus at the center of the atom.

• Option A is incorrect because not all alpha particles bounced back; most passed through.
• Option C is incorrect as most alpha particles did go through the gold foil.
• Option D is incorrect because while most went straight, some bounced back, so not all went straight.
• Option B is correct as the observation of some alpha particles bouncing back was the surprising result that led to the discovery of the atomic nucleus.

Answer:

B. Some of the alpha particles shot at the gold foil bounced back.