The answer is attached :)
Inert means unreactive in nature or un reactive in there normal or natural state
and noble gas has there outermost shell electron filled up they complete there duplet or oclet valency state that why there inert in there natural state
Round 89 to 90 then divide by 4. so its 24.
Polonium has an atomic number of 84 meaning it has 84 protons. Usually, this means there would also be 84 electrons in a normal element. A -3 charge means that there are 3 more negative electrons that positive protons so the overall number of electrons would be 87.