How many corrdinated water molecule(s) is//are present in brown ring complex ? .

Explanation

To determine how many coordinated water molecules are present in the brown ring complex, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Brown Ring Complex**:
The brown ring complex is formed by the reaction of ferrous sulfate (FeSO4) with nitric oxide (NO) in the presence of water. The general formula for the brown ring complex can be represented as [Fe(H2O)5NO]SO4.

2. **Write the Reaction**:
The reaction can be summarized as:
\[ \text{FeSO}_4 + \text{NO} + \text{H}_2\text{O} \rightarrow [\text{Fe(H}_2\text{O)}_5\text{NO}]^{2+} + \text{SO}_4^{2-} \]

3. **Determine the Coordination Number**:
The coordination number of a metal ion in a complex refers to the number of ligand atoms that are directly bonded to the central metal ion. In the case of the brown ring complex, iron (Fe) is the central metal ion.

4. **Identify the Ligands**:
In the brown ring complex, the ligands are:
- 5 water molecules (H2O)
- 1 nitric oxide (NO) molecule

5. **Calculate the Total Number of Coordinated Water Molecules**:
Since there are 5 water molecules coordinated to the iron ion, we conclude that:
\[ \text{Number of coordinated water molecules} = 5 \]

6. **Final Answer**:
Therefore, the number of coordinated water molecules present in the brown ring complex is **5**.