State one major difference between having a nitrogen atom in a ring structure and having an oxygen atom in that structure

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One major difference between having a Nitrogen atom in a ring structure and having an oxygen atom in that structure would be that Oxygen atoms are electron attractors by resonance and Nitrogen atoms are electron donors by resonance. 
In a ring structure, Nitrogen can donate an electron and become positively charged and Oxygen can attract an electron from the ring to become negatively charged, as electrons relocate in resonance structures. This can produce changes in terms of reactivity and stability of the ring.
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Answer : option a) 84explanation :

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.