A cobaltamine has the formula CoCI₃ . xNH₃. This when reacted with AgNO₃ solution, one third of the chloride is precipitated. It can have the structure

a) [Co(NH₃)₆]CI₃
b) [Co(NH₃)₅]CI₂
c) [Co(NH₃)₄CI₂]CI
d) [Co(NH₃)₅H₂O]CI₃