Which of the following statement is incorrect?

Options

A. `Al_2O_3`, cannot be reduced into Al by `Cr_2O_3`
B. Ca is stronger reducing agent than Mg
C. At 673 k, CO is poor reducing agent than carbon
D. All of these

Answer

To determine which statement is incorrect among the given options, we will analyze each statement based on our knowledge of chemistry, particularly focusing on the reactivity series and the properties of reducing agents.

### Step-by-Step Solution:

1. **Understanding the Reactivity Series**:
- The reactivity series is a list of metals arranged in order of decreasing reactivity. Metals higher in the series can displace those lower in the series from their compounds.
- Aluminum (Al) is higher in the reactivity series compared to chromium (Cr). Therefore, aluminum cannot be reduced by chromium compounds.

2. **Analyzing Statement 1**:
- The statement "Al2O3 cannot be reduced into aluminum by Cr2O3" is correct because chromium is less reactive than aluminum. Thus, this statement is not the incorrect one we are looking for.

3. **Understanding Reducing Agents**:
- A reducing agent is a substance that donates electrons in a chemical reaction and is oxidized in the process. The strength of a reducing agent generally increases as you move down a group in the periodic table due to the increase in atomic size and the ease of losing electrons.

4. **Analyzing Statement 2**:
- The statement "Ca is a stronger reducing agent than magnesium" is also correct. Calcium (Ca) is below magnesium (Mg) in the group and is indeed a stronger reducing agent.

5. **Analyzing Statement 3**:
- The statement "At 673 Kelvin, CO is a poor reducing agent than carbon" needs careful consideration. At this temperature, carbon monoxide (CO) is actually a better reducing agent than carbon (C) because the enthalpy change for the reaction involving CO and CO2 is more favorable than that of carbon. Therefore, this statement is incorrect.

6. **Conclusion**:
- The incorrect statement is "At 673 Kelvin, CO is a poor reducing agent than carbon." Hence, the answer is option C.

### Final Answer:
The incorrect statement is: "At 673 Kelvin, CO is a poor reducing agent than carbon."

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