Weight of `SO_(3)` taken = 200 g
Number of moles of `SO_(3) = 200/("GMW of "SO_(3))=200/80 = 2.5 ` moles
Volume occupied by 1 mole of gas is 22.4 L, at STP
Volume occupied by the given amount of gas = `2.5 xx 22.4 = 56` L
Number of molecules present in 1 mole of gas = ` 6.023 xx 10^(23)`
Number of molecules present in the given amount of gas = `2.5 xx 6.023 xx 10^(23) = 15.05 xx 10^(23)` molecules