Which particle of the atom is the smallest and has the least mass? a) all are the same size b) protons c) electrons d) neutrons

Protons and neutrons have very nearly the same mass ... equal to the mass of more than 1800 electrons.

Neutrinos have virtually zero mass .

The "size" of any of these is meaningless. They're waves, not little ping-pong balls

If you MUST make a choice, pick C.

the rearrangement of particles in a physical change. hope this