A certain radioactive atom has 90 protons and 142 neutrons. If this atom undergoes alpha decay, what is the mass number of the daughter atom? The mass number of the daughter atom is .

228

Explanation:

alpha decay is removing alpha particle

2 number of protons, 4 mass number = 2 protons + 2 neutrons

We have

      90 protons and 142 neutrons

      - 2 protons         -  2 neutrons

      88 protons         140 neutrons

Mass number of new (daughter) atom = 88 +140 = 228

a