Identify the incorrect statement.

Options

A. `Cr^(2+) (d^4)` is a stronger reducing agent than `Fe^(2+) (d^6)` in water
B. The transition metals and their compounds are known for their catalytic activity due to their ability to adopt multiple oxidation states and to form complexes.
C. Interstitial compounds are those that are formed when small atoms like H,C, orN are trapped inside the crystal lattices of metals.
D. The oxidation states of chromium in `CrO_4^(2-) and Cr_2o_7^(2-)` are not the same.

Answer

To identify the incorrect statement from the provided options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyzing the First Statement:**
- The statement claims that Cr²⁺ in the d⁴ state acts as a stronger reducing agent than Fe²⁺ in the d⁶ state in water.
- **Explanation:** Cr²⁺ can easily oxidize to Cr³⁺, which is a stable state (d³ configuration). The presence of unpaired electrons in Cr²⁺ allows it to act as a stronger reducing agent compared to Fe²⁺, which oxidizes to Fe³⁺ (d⁵ configuration). The d⁵ state is stable due to half-filled orbitals, making it less likely to oxidize.
- **Conclusion:** This statement is correct.

2. **Analyzing the Second Statement:**
- The statement asserts that metals and their compounds are known for their catalytic activity due to their ability to adopt multiple oxidation states and form complexes.
- **Explanation:** Transition metals can exist in multiple oxidation states due to their d-electrons, which allows them to form various complexes and act as catalysts in different reactions.
- **Conclusion:** This statement is correct.

3. **Analyzing the Third Statement:**
- The statement describes interstitial compounds as those where small atoms (like hydrogen, carbon, nitrogen) are trapped inside the crystal lattice of metals.
- **Explanation:** Interstitial compounds indeed consist of small atoms fitting into the spaces of the metal lattice, which can increase the melting point and retain metallic properties. However, these compounds can exhibit different chemical properties compared to pure metals.
- **Conclusion:** This statement is correct.

4. **Analyzing the Fourth Statement:**
- The statement claims that the oxidation state of chromium is not the same in CrO₄²⁻ and Cr₂O₇²⁻.
- **Calculation for CrO₄²⁻:**
- Let the oxidation state of Cr be x.
- The equation is: x + 4(-2) = -2 → x - 8 = -2 → x = +6.
- **Calculation for Cr₂O₇²⁻:**
- Let the oxidation state of Cr be x.
- The equation is: 2x + 7(-2) = -2 → 2x - 14 = -2 → 2x = 12 → x = +6.
- **Conclusion:** Both compounds have chromium in the +6 oxidation state, making the statement incorrect.

### Final Conclusion:
The incorrect statement is the fourth one, which claims that the oxidation state of chromium is not the same in CrO₄²⁻ and Cr₂O₇²⁻. In reality, both have chromium in the +6 oxidation state.