Answer
C
Work Step by Step
$x\ AgNO_3(aq)+1\ Na_2CO_3(aq)\rightarrow y\ Ag_2CO_3(s)+z\ NaNO_3(aq)$
Balancing:
Na: $2=z$
N: $x=z=2$
Ag: $x=2\times y\rightarrow y=1$
Removing the $NaNO_3$ ions:
$2\ Ag^+(aq)+1 CO_3^{2-}(aq)\rightarrow 1\ Ag_2CO_3(s)$