An isotope undergoes radioactive decay. the new isotope that forms has an atomic number that is 2 less than the original isotope’s. which kind of decay has occurred, and how do you know? alpha decay because alpha particles have a large mass beta decay because beta particles can have negative charge alpha decay because alpha particles have two protons and two neutrons gamma decay because gamma rays are photons

alpha decay because alpha particles have two protons and two neutrons

Explanation:

An alpha particle has a nucleus which is made up of 2 protons and 2 neutrons. It is actually a Helium cation.

A nuclear reaction involves the nucleus and the elementary particles contained within them.

If an isotope undergoes radioactive decay and the new isotope that forms has an atomic number that is 2 less than the original isotope,it shows an alpha decay has occurred.

The atomic number is the number of protons and it is the same as the number electrons for a neutral atom.

In this isotope, the reaction must have involved loss of two protons from the nucleus. The atomic number comes two less than that original one.

The mass number i.e number of proton + neutron is 4. Therefore, the mass number of the isotope would also decrease by 4.

This is to obey the law of conservation by mass.