The limiting reagent is Copper (Cu).
Explanation:
The balanced equation is:
Cu + 2AgNO3 -----> Cu(NO3)2 + 2Ag
[tex]5.50 mol Cu \times (\frac{1.00 mol Cu}{2.00 mol AgNO3} )[/tex] = 2.75 mol Cu.
Since there are only 2.50 mol Cu, copper is the limiting reactant, because, with that quantity of copper, only 2.50 mol AgNO3 will be reacted.