When conc. HCl is added to the solution of `Cr(NO_(3))_(2)`, then it slowly turns green due to formation of the following

Options

A. `CrCl_(2)`
B. `Cr_(2)O_(3)`
C. `CrO_(4)`
D. Chlorocomplex

Answer

To solve the question regarding the color change when concentrated HCl is added to a solution of Cr(NO3)2, let's break down the process step by step.

### Step-by-Step Solution:

1. **Identify the Reactants:**
- The reactants are Cr(NO3)2 (chromium(II) nitrate) and concentrated HCl (hydrochloric acid).

2. **Understand the Reaction:**
- When concentrated HCl is added to Cr(NO3)2, a complex ion is formed. The chromium ion in Cr(NO3)2 can form a complex with water molecules and chloride ions from HCl.

3. **Formation of the Complex:**
- The chromium ion (Cr^2+) can coordinate with water molecules and chloride ions. The reaction can be represented as:
\[ \text{Cr(NO}_3\text{)}_2 + 6 \text{H}_2\text{O} + 3 \text{HCl} \rightarrow \text{[Cr(H}_2\text{O)}_6]^{3+} + 3 \text{NO}_3^{-} + 3 \text{Cl}^- \]
- Here, the chromium ion is surrounded by six water molecules, forming a hexaaquachromium(II) complex, which can further react with chloride ions.

4. **Color Change Observation:**
- The solution slowly turns green due to the formation of the chloro complex, which is a result of the interaction between chromium ions and chloride ions. The specific chloro complex formed is [CrCl3(H2O)3], which imparts a green color to the solution.

5. **Conclusion:**
- The green color observed is due to the formation of the chloro complex of chromium. Therefore, the correct answer to the question is the chloro complex.

### Final Answer:
The solution turns green due to the formation of the chloro complex.