1.

The reactivity of an element is based on its .

protons

electrons

2.

electrons are the most important electrons to an atom.

Outer

Inner

3.

refers to how reactive a substance is with oxygen.

Reduction

Combustibility

the answer would be b i believe

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.