Which of the following complexes is non-conducting?

CoCl₃.3NH₃

The correct answer is option 1. \(CoCl_3.3NH_3\)

The non-conducting complex among the given options is \( \text{CoCl}_3 \cdot 3\text{NH}_3 \)In this complex, \( \text{CoCl}_3 \cdot 3\text{NH}_3 \), the coordination number of cobalt is 6, and it forms a complex with 3 ammonia (\( \text{NH}_3 \)) molecules. Since the number of ammonia molecules is less than the coordination number, there will be some uncoordinated ions (\( \text{CoCl}_3 \)) present in the solid. These uncoordinated ions make the complex non-conductive in the solid state.

On the other hand, the other options have the same or more number of ligands (\( \text{NH}_3 \)) as compared to the coordination number, resulting in fully coordinated complexes, which are generally more likely to be conducting.