Answer: The correct answer is decreased by two.
Step-by-step explanation:
Alpha particle is emitted when a radioactive isotope undergoes alpha decay process. In this process a heavier particle decays into a lighter particle with the release of alpha particle. The alpha particle carries a mass of 4 units and a charge of +2 units.
The atomic number of the atom gets reduced by 2 units and atomic mass of the same atom gets reduced by 4 units.
The equation representing alpha decay process is:
![_Z^A\textrm{X}\rightarrow _(Z-2)^(A-4)\textrm{Y}+_2^4\alpha](https://img.qammunity.org/2019/formulas/chemistry/high-school/kb843legtg9h2t3t7b8pv29l2emurat9zu.png)
Hence, the correct answer is decreased by two.