The chemical equation is
[tex]2Ag+SO_4\to Ag_2SO_4[/tex]According to the equation, the ratio between Ag and the product is 2:1.
So, if we have 0.50 moles of Ag, then we use the ratio to find the moles of the product.
[tex]0.50\text{mol(Ag)}\cdot\frac{1\text{mol(Ag}_2SO_4)}{2\text{moles(Ag)}}=0.25\text{mol(Ag}_2SO_4)[/tex]Therefore, there can be formed 0.25 moles of Ag2SO4 from 0.50 mol of Ag.