What is the change in atomic mass when an atom emits an alpha particle? A. decreases by 2 B. decreases by 1 C. decreases by 4 D. remains the same

Answer is "C"

alpha decay is an emission of ₂⁴He nucleus. If an element undergoes an alpha decay, the mass of the daughter nucleus formed is reduced by 4 compared to mass of parent atom and atomic number is reduced by 2 compared to atomic number of parent atom.