From the equation,
1 mol of Zn reacts with 2 mol of AgNO3
5 mol of Zn reacts with 2/1 × 5 = 10 mol of AgNO3
Since there is only 8.0 mol of AgNO3 present, Zn is in excess.
To deduce how many moles of Ag is formed we will use the 8 mol of AgNO3 as it is the limiting reagent.
2 mol of AgNO3 form 2 mol of Ag
8 mol of AgNO3 from 2/2 × 8 = 8 mol of Ag