When aqueous sodium hydroxide was added to an aqueous solution of X, a green precipitate, insoluble in an excess of aqueous sodium hydroxide, was formed. When aqueous barium nitrate was added to a second sample of aqueous X a white precipitate was obtained. Which one of the following could be X?

Options

A. `FeCl_(2)`
B. `FeSO_4`
C. `CrCl_3`
D. `Cr_2(SO_4)_(3)`

Answer

To solve the question, we need to analyze the reactions that occur when aqueous sodium hydroxide and aqueous barium nitrate are added to the solution of X.

### Step-by-Step Solution:

1. **Identify the Reaction with Sodium Hydroxide:**
- When aqueous sodium hydroxide (NaOH) is added to the solution X, a green precipitate is formed that is insoluble in excess NaOH. This indicates the formation of a hydroxide of a metal that is not soluble in excess hydroxide.
- The green precipitate suggests the presence of ferrous ions (Fe²⁺), which form ferrous hydroxide (Fe(OH)₂) when reacted with NaOH.

2. **Write the Reaction:**
- The reaction can be represented as:
\[ \text{FeSO}_4 (aq) + 2 \text{NaOH} (aq) \rightarrow \text{Fe(OH)}_2 (s) + \text{Na}_2\text{SO}_4 (aq) \]
- Here, Fe(OH)₂ is the green precipitate formed.

3. **Identify the Reaction with Barium Nitrate:**
- When aqueous barium nitrate (Ba(NO₃)₂) is added to a second sample of solution X, a white precipitate is formed. This indicates the formation of barium sulfate (BaSO₄), which is known to be a white precipitate.
- This suggests that the solution X contains sulfate ions (SO₄²⁻).

4. **Write the Reaction:**
- The reaction can be represented as:
\[ \text{FeSO}_4 (aq) + \text{Ba(NO}_3)_2 (aq) \rightarrow \text{BaSO}_4 (s) + \text{Fe(NO}_3)_2 (aq) \]
- Here, BaSO₄ is the white precipitate formed.

5. **Conclusion:**
- Based on the reactions observed, the only compound that fits the criteria is ferrous sulfate (FeSO₄). Therefore, the identity of solution X is ferrous sulfate.

### Final Answer:
The solution X could be **ferrous sulfate (FeSO₄)**.

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