The CFSE for octahedral  CoCl64- is 18,000 cm-1 . The CFSE for tetrahedral will be CoCl42-

1. 6000 cm-1

2. 16,000 cm-1

3. 18,000 cm-1

4. 8,000 cm-1

Hint:  \(\Delta_{t} =\frac{4}{9}\Delta_{o} \) 

The relation between \( \Delta_{t}\) and \(\Delta_{o} \) is \(\Delta_{t} =\frac{4}{9}\Delta_{o} \)

Where,0 CFSE for octahedral complex, t = CFSE for tetrahedral complex

According to question, 0=18,000 cm-1t=49 0=49×18,000 cm-1=4×2,000 cm-1=8,000 cm-1

Hence , correct choice is option fourth