A solution containing $2.675\text{g}$ of ${\text{CoCl}}_3\cdot 6{\text{NH}}_3$ (molar mass $=267.5{\text{g mol}}^{-1}$) is passed through a cation exchanger. The chloride ions obtained in solution were treated with excess of ${\text{AgNO}}_3$ to give $4.78\text{g}$ of $\text{AgCl}$ (molar mass $=143.5{\text{g mol}}^{-1}$). The formula of the complex is (At. Mass of $\text{Ag}=108\text{u}$):

1. A
   $[\text{Co}({\text{NH}}_3{)}_6]{\text{Cl}}_3$
2. B
   $[{\text{CoCl}}_2({\text{NH}}_3{)}_4]\text{Cl}$
3. C
   $[{\text{CoCl}}_3({\text{NH}}_3{)}_3]$
4. D
   $[\text{CoCl}({\text{NH}}_3{)}_5]{\text{Cl}}_2$