Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
A radioactive nucleus consists of an unstable assembly of protons and neutrons which becomes more stable by emitting an alpha, a beta particle, or a gamma photon.
Atoms are radioactive if their nuclei are unstable and spontaneously (and random) emit various particles α, β, and/or γ radiations.
Three crucial forms of Radioactivity:
Gamma Decay-(Photons having high energy are throw down).
Beta Decay-(Discharge consists of Electrons).
Alpha Decay-(Discharge consists of a Helium nucleus).
EXPLANATION:
From above it is clear that the that an alpha particle consist of two proton and two neutrons and they are tightly bound.
An alpha-particle is identical to the nucleus of a helium atom. Therefore option 1 is correct.