When a reagent (X) reacts with `Fe^(3+)` salt solution turnsred due to the formation of a compound (Y). This reagent cause no change in colour with `Fe^(2+)` salt solution. Compound (X) and (Y) are respectively:

Options

A. `NH_(4)SCN and Fe(SCN)_(3)`
B. `K_(4)[Fe(CN)_(6)] and FeSO_(4)`
C. `Na_(2)HPO_(4) and FeSO_(4)`
D. `K_(3)[Fe(CN)_(6)] and K_(2)Fe[Fe(CN)_(6)]`

Explanation

To solve the question, we need to identify the reagent (X) and the compound (Y) formed when reagent X reacts with Fe³⁺ ions. Here's a step-by-step breakdown of the solution:

### Step 1: Understanding the Reaction
The question states that when a reagent (X) reacts with Fe³⁺ salt solution, it turns red due to the formation of compound (Y). Additionally, it mentions that this reagent does not cause any color change with Fe²⁺ salt solution.

### Step 2: Identifying the Reagent (X)
A well-known reagent that reacts with Fe³⁺ ions to produce a red-colored complex is ammonium thiocyanate (NH₄SCN). When NH₄SCN is added to a solution containing Fe³⁺ ions, it forms a complex ion, which is responsible for the red color.

### Step 3: Writing the Reaction
The reaction can be represented as follows:
\[ \text{Fe}^{3+} + 3 \text{NH}_4\text{SCN} \rightarrow \text{Fe(SCN)}^{2+} + 3 \text{NH}_4^{+} \]
The complex ion formed, \(\text{Fe(SCN)}^{2+}\), is known for its blood-red color.

### Step 4: Identifying the Compound (Y)
From the reaction, we see that the compound (Y) formed is \(\text{Fe(SCN)}^{2+}\), which is the blood-red colored solution mentioned in the question.

### Step 5: Confirming the Behavior with Fe²⁺
The question also states that reagent (X) does not cause any color change with Fe²⁺ ions. This is consistent because ammonium thiocyanate does not react with Fe²⁺ ions in a way that produces a colored complex.

### Conclusion
Based on the above analysis, we can conclude:
- Reagent (X) is **Ammonium Thiocyanate (NH₄SCN)**
- Compound (Y) is **Iron(III) Thiocyanate (\(\text{Fe(SCN)}^{2+}\))**

### Final Answer
- **Reagent (X): NH₄SCN**
- **Compound (Y): \(\text{Fe(SCN)}^{2+}\)**