Answer: In alpha decay, an alpha particle is emitted.
Step-by-step explanation:
Alpha decay is defined as the decay process where an alpha particle is emitted. In this process, a heavier nuclei decays into a lighter nuclei. The alpha particle emitted carries a charge of +2 units and a mass of 4 units.
The emitted alpha particle is also known as helium nucleus.
In this decay process, the atomic number of the parent atom decreases by 2 units and the mass number decreases by 4 units.
The chemical equation for alpha decay process follows:

Hence, in alpha decay, an alpha particle is emitted.