The period of time needed for a radioisotope to lose one-half of its activity is known as that isotopes

Explanation:

The radioactive scattering technique is called radioactive degradation. For each radioactive isotope, the natural radioactive cycle is special and is determined by a period of time termed a half-life. One half-life was its time needed to experience radioactivity for half of both the radioactive nuclei.

50.23 i believe is correct but don't quote me on that.

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.