how many atoms are present in 0.25 mole of so​_​3?

First we'll find the no. of molecules in the given no of moles, 1 mole of SO3 = NA(Avogadro No) molecules 0.25 moles = (1/4)*NA molecules To find No. Of atoms, we'll multiply no. Of molecules by its atomicity. No. Of atoms = 4*(1/4)*NA = NA = 6.022*10^23