Chemical Equations Need to Be Balanced Not Only in Terms $\mathrm { Sn } ^ { 2 + }$

Chemical equations need to be balanced not only in terms of the number of atoms,but also by the charge.In other words,just as there should be the same number of atoms before and after the arrow of an equation,there should be the same charge.What set of coefficients is necessary to balance the following chemical equation? ________ $\mathrm { Sn } ^ { 2 + }$ + ________ Ag ? ________ Sn + ________ Ag?

A) 1,2,1,2
B) 1,1,1,2
C) 1,2,2,2
D) 1,1,2,1