Answer:
The nucleus of the atom looses two protons and two neutrons.
Step-by-step explanation:
In Chemistry, an alpha particle which is typically a helium nucleus has an atomic mass (number of nucleons) of four (4) i.e two protons and two neutrons. Therefore, the ejection of an alpha particle by any chemical element simply means that, the mass number of that particular chemical element would be reduced by four (4).
Basically, this process is referred to as an alpha decay and can be defined as a radioactive disintegration of a chemical element that causes it to emit an alpha particle and as a result reducing its mass number by four (4).
Hence, when an alpha particle is emitted, the nucleus of the atom looses two protons and two neutrons.
This ultimately implies that, when an atom of a radioactive element such as Uranium-238, its mass number is reduced by four (4) to form Thorium-234.