Question

Reason for deflection of alpha partile in rutherford experiment?

Answer 1

Because it bumped into a heavy nucleus.............

Explanation:

See this older answer.

Rutherford used a variety of metal films to perform his experiment. Gold is very malleable amongst metals, which means that it can be beaten out into a very thin sheet. The fact that an heavy `alpha-"particle"` could bounce off the (infinitesimally) THIN gold sheet, right back at the `alpha-"particle"` emitter, was an extremely unexpected result.