To investigate the effect of acid rain on the germination of the seeds, a student uses four containers of soil with 25 pea seeds planted in each. Rainwater was collected and used for the investigation. The chart shows how many seeds germinated in each container. Which container is the control for the experiment?

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.