$A$ coordination complex compound of cobalt has a molecular formula containing five ammonia molecules,one nitro group,and two chlorine atoms for one cobalt atom. One mole of this compound produces three moles of ions in an aqueous solution,and upon reacting with an excess of $AgNO_3$,it forms $AgCl$ precipitate. The ionic formula for this complex would be:

• A
  $[Co(NH_3)_5(NO_2)]Cl_2$
• B
  $[Co(NH_3)_5Cl][Cl(NO_2)]$
• C
  $[Co(NH_3)_4(NO_2)Cl][(NH_3)Cl]$
• D
  $[Co(NH_3)_5][(NO_2)_2Cl_2]$