Reaction of Copper with Mercuric Nitrate is as follow,
                       Cu  +  Hg(NO₃)₂    →    Cu(NO₃)₂  +  Hg
According to equation,
                            1 Mole of Cu reacts to form  =  1 Mole of Hg
So,
           1.20 Moles of Cu will react to produce  =  X Moles of Hg
Solving for X,
                                   X  =  (1.20 mol × 1 mol) ÷ 1 mol
                                   X  =  1.20 mol of Hg
Result:
          1.20 mole of Cu when reacted with mercuric nitrate produces 1.20 moles of Hg.