Vitamin A has a molecular formula C20 H30 O. The number of vitamin A molecules in 500mg of its capsule will be:

Actually that is 500 mg so we first have to convert it into grams
And then find the molar mass of Vitamin A formula which is 286 g.

Now 286g contain 6.023*1023

So 0.5 g contain how much ?

So we simply multiply the NA with the 0.5 and divided by 286

Which gives us about 1.05*10^21

It will appear as o2(g) as a reactant