Assertion: Rutherford's experiment concluded that the positive charge is not uniformly distributed in an atom. 

Reason: Rutherford’s model of the atom proposed that a very tiny nucleus is present inside the atom and electrons revolve around this nucleus. 

Both assertion and reason are true but the reason is not the correct explanation of the assertion.

Assertion: In Rutherford’s alpha-scattering experiment, it was observed that few alpha particles were deflected by the gold sheet by a very small angle, hence the positive charge is not uniformly distributed in an atom. 

Reason: Rutherford proposed that the positive charge and most of the mass of an atom are concentrated in a very small volume, and he called this region a nucleus. He proposed that negatively charged electrons revolve around the nucleus at very high speed in circular paths. He called these circular paths orbits.