$A$ chemist wants to determine the molecular geometry of the $[CoCl_4]^{2-}$ ion. Which of the following gives the best suggestion for a measurement and for the interpretation of that measurement?

• A
  Using absorption spectroscopy,measure $\lambda_{max}$ then calculate $\Delta_0$ for octahedral geometry
• B
  Measure the molecule's magnetic moment and use the result to estimate the number of unpaired spins in the molecule. If this number is low,the geometry is likely to be square planar; otherwise,it is likely to be tetrahedral
• C
  Measure the molecule's magnetic moment and use the result to estimate the number of unpaired spins in the molecule. If this number is low,the geometry is likely to be tetrahedral; otherwise,it is likely to be square planar
• D
  Measure the molecule's magnetic moment and use the result to estimate the number of unpaired spins in the molecule. If this number is low,the geometry is likely to be tetrahedral; otherwise,it is likely to be octahedral