Chem q

I think of it as standardising the value. Because mass isnt technically comparable, like 5g of oxygen doesnt contain the same number of particles as 5g of sodium. So that why you divide by Mr to get moles, then find moles of the product. And then mass of product using the number moles. Then, you can find % yield

Why can't you do actual mass divided by theoretical like 0.98 divided by 1. I understand how to get the answer A but why do we have to work out the moles and not just used mass thanks