$A$ solution contains $2.675 \ g$ of $CoCl_3 \cdot 6NH_3$ $(M = 267.5 \ g/mol)$. When passed through a cation exchanger,the chloride ions liberated are treated with excess $AgNO_3$ to yield $4.78 \ g$ of $AgCl$ $(M = 143.5 \ g/mol)$. What is the formula of the coordination compound?

• A
  $[Co(NH_3)_6]Cl_3$
• B
  $[CoCl(NH_3)_5]Cl_2$
• C
  $[CoCl_3(NH_3)_3]$
• D
  $[CoCl_2(NH_3)_4]Cl$