An alpha particle is composed of

A. nothing

B. two protons and two neutrons

C. one proton and no neutrons

D. one neutron no protons

B. Two protons and two neutrons

Answer: B. two protons and two neutrons

Explanation: Alpha rays are fast moving streams of positively charged particles which are shown to be helium nuclei represented by 4He2, having a mass number of 4, i. e., having 2 protons and 2 neutrons. Mass number of an element is the sum of the number of protons and neutrons in the nucleus of an atom. A helium atom has 2 protons and 2 neutrons in its atom.