Question

After a nucleus undergoes radioactive decay, its new mass number is:

Answer 1

Radioactive "decay" means particles and stuff shoot OUT of a nucleus.
After that happens, there's less stuff in the nucleus than there was before.
So the new mass number is always less than the original mass number.

Answer 2

Answer: The new mass number is never more than its original mass number

Explanation:

Radioactive decay is defined as the process in which an unstable nuclei breaks down into stable nuclei via various methods.

An isotope undergoes a radioactive decay to attain stability.

There are many decay processes by which a parent nucleus can undergo decay. They are:

Alpha decay is defined as the decay process in which alpha particle is released. In this process, a heavier nuclei decays into a lighter nuclei. The alpha particle released carries a charge of +2 units and a mass of 4 units.

$_Z^A\textrm{X}\rightarrow _{Z-2}^{A-4}\textrm{Y}+_2^4\alpha$

Beta decay is defined as the decay process in which a neutron gets converted to a proton and an electron.  In this decay process, beta particle is emitted. The emitted particle carries a charge of -1 units and has a mass of 0 units. The released beta particle is also known as electron.

$_Z^A\textrm{X}\rightarrow _{Z+1}^A\textrm{Y}+_{-1}^0\beta$

Gamma decay is defined as the decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. This decay releases $\gamma -radiations$. This process does not change the mass number.

$_A^Z\textrm{X}^*\rightarrow _A^Z\textrm{X}+_0^0\gamma$

For every decay process, the mass number will either remain same or the mass number of new isotope will be less than the parent isotope but not more than the original mass number.

Hence, the new mass number is never more than its original mass number