An alpha particle is identical to a). a neutron b) a helium nucleus c) an electron d) a hydrogen nucleus

Alpha particles, also called alpha ray or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways.

Composition: 2 protons, 2 neutrons

Mass: 6.644657230(82)×10−27 kg; 4.0015061...

Electric charge: +2 e

Symbol: α, α2+, He2+

b) a helium nucleus

Explanation:

Alpha (α) particles are emissions from a radioactive nucleus, they occur when the nucleus loses 4 units of mass and 2 of atomic number.

They have less penetration than beta or gamma radiation and are composed of two protons and two neutrons, without electrons. That is why it has a +2 charge corresponding to the proton charge.  

He nuclei are composed of 2 protons and two neutrons. This is why alpha particles are identical to their nucleus.

The Helium present in the atmosphere is the product of the emission of alpha particles. For example from the Radon gas that is mostly present in soil, water and rocks.