A solution containing 2.615 g of CoCl₃ 6NH₃ (molar mass = 267 g mol^-1) is passed through a cation exchanger' The chloride ions obtained in solution were treated with excess of AgNO₃ to give 4.78 g of AgCl. The formula of the complex is:

• A

  $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_6\right]{\mathrm{Cl}}_3$

• B

  ${\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_3{\mathrm{Cl}}_3\right]}_3{\mathrm{NH}}_3$

• C

  $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Cl}}_2\right]{\mathrm{Cl}}_2{\mathrm{NH}}_3$

• D

  $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_5\mathrm{Cl}\right]{\mathrm{Cl}}_2{\mathrm{NH}}_3$