Which of the following is blue?

Options

A. `Co[Hg(SCN)_(4)]`
B. `Ni(d m g)_(2)`
C. `Cu_(2)[Fe(CN)_(6)]`
D. `Fe(SCN)_(3)`

Answer

To determine which of the given complexes is blue, we will analyze each of the options provided:

1. **CO(HG)(SCN)₄**: This complex contains cobalt (Co) and is known to exhibit a blue color. Therefore, this complex is blue.

2. **Ni(DMG)₂**: This complex contains nickel (Ni) and dimethylglyoxime (DMG). It is known to produce a red color, not blue.

3. **Cu₂[Fe(CN)₆]**: This complex is formed when copper (Cu²⁺) reacts with potassium ferrocyanide (K₄[Fe(CN)₆]). The resulting complex has a chocolate color, which is not blue.

4. **Fe(SCN)₃**: This complex contains iron (Fe) and thiocyanate (SCN). It is known to have a blood red color, again not blue.

After evaluating all the options, we conclude that the only complex that is blue is:

**Answer: CO(HG)(SCN)₄ is blue.**