L 2.3.4 Quiz: Calculating the Reaction Rate Question 7 of 10
Why does the reaction rate decrease as the reaction progresses?
A. The temperature begins to go down.
B. The activation energy goes up.
C. The rate constant changes over time.
O D. There are fewer reactants left to collide.
SUBMIT

the answer your looking for is c).

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.