Answer:
A. A neutron transforms into a proton and an electron.
Explanation:
Yes, this is what happens in β decay.
![_(0)^(1)\text{n} \rightarrow _(1)^(1)\text{H} + _(-1)^(0)\text{e}](https://img.qammunity.org/2019/formulas/chemistry/high-school/ybffx05gvjpxffrw9ij8hukwx2iygakwx2.png)
The proton stays in the nucleus and increases the atomic number by one, and the electron is ejected from the nucleus.
B is wrong. This is impossible because charge is not conserved. You can’t convert a positive particle into a negative particle.
C is wrong. Again, this is impossible because charge is not conserved.
D is wrong. Charge is conserved, but this is the process of electron capture.