The flocculating power of \([Fe(CN)_6]^{4-}\) is higher than \(PO_4^{3-}\) ion because:

It has higher negative charge

The correct answer is option 2. It has higher negative charge.

The flocculating power of an ion refers to its ability to cause the precipitation or coagulation of colloidal particles in a solution. This is explained by the Schulze-Hardy rule, which states that the effectiveness of an ion in coagulating a colloid is proportional to the magnitude of the charge on the ion.

Higher charge ions have a stronger ability to neutralize the charges on colloidal particles, thus facilitating the process of coagulation or flocculation.

Let us analyze the given ions:

\([Fe(CN)_6]^{4-}\): This ion has a 4- charge.

\(PO_4^{3-}\): This ion has a 3- charge.

According to the Schulze-Hardy rule, the greater the negative charge on the ion, the greater its flocculating power. Since \([Fe(CN)_6]^{4-}\) has a higher negative charge compared to \(PO_4^{3-}\), it will have a stronger flocculating power.

Why the other options are not correct:

1. It is a complex ion: While \([Fe(CN)_6]^{4-}\) is a complex ion, the complex nature of the ion does not directly influence its flocculating power as much as the charge does.

3. It involves metal ion in it: The presence of a metal ion in \([Fe(CN)_6]^{4-}\) does not directly affect the flocculating power. The charge on the ion is the key factor here.

4. It has a strong ligand field: The strength of the ligand field in the complex \([Fe(CN)_6]^{4-}\) does not impact its ability to flocculate colloids. Again, the charge is the most important factor in determining flocculating power.

Conclusion:

The higher flocculating power of \([Fe(CN)_6]^{4-}\) compared to \(PO_4^{3-}\) is due to its higher negative charge.

Therefore, the correct answer is 2. It has higher negative charge.