25) In a certain area where there are many farms, the groundwater levels have dropped by as much as 10 m over a period of 30 years. The main cause behind this is MOST LIKELY A) the evaporation of water from aquifers.

B) the excessive pumping of water through wells.

C) the leakage of fertilizers from the farms into the aquifer.

D) the construction of a dam to divert water into a reservoir.
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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.