-4
Explanation:
If a radioactive isotope undergoes alpha decay, it's mass number will change by -4.
The mass number of a nuclei is the sum of its number of protons and neutrons.
An alpha particle is similar of a helium atom:
⁴₂He
The atom above is made up of:
mass number = 4
Atomic number = 2
Number of protons = 2
Number of neutrons = 2
Number of electrons = 2
If a substance is undergoing radioactive decay, the mass number of the product will decrease by 4 and the atomic number will decrease by 2.
In nuclear equations, mass and atomic numbers are usually conserved.
learn more:
Transmutation brainly.com/question/3433940
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