Final answer:
The source of alpha particles in Rutherford's scattering experiment was helium nucleus.
Step-by-step explanation:
The source of alpha particles in Rutherford's scattering experiment was c. Helium Nucleus. In the experiment, alpha particles, which are helium nuclei consisting of two protons and two neutrons, were emitted from a radioactive source and directed towards a thin gold foil. The scattering of alpha particles from the gold foil provided evidence for the size and mass of the nucleus.