Which of the following statements is not correct?

Options

A. Copper liberates hydrogen from acids.
B. In higher oxidation states, manganese forms stable compounds with oxygen and fluorine.
C. `Mn^(3+) and Co^(3+)` are oxidising agents in aqueous solution.
D. `Ti^(2+) and Cr^(2+)` are reducing agents in aqueous solution.

Explanation

To determine which statement is not correct among the options provided, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze Statement 1: "Copper liberates hydrogen from acids."**
- Copper (Cu) is a transition metal with a standard reduction potential greater than that of hydrogen ions (H⁺). The standard reduction potential for copper is positive, while that for hydrogen is zero. This means that copper cannot reduce hydrogen ions to liberate hydrogen gas.
- Therefore, this statement is **incorrect**.

2. **Analyze Statement 2: "The higher oxidation state of manganese forms stable compounds with oxygen and chlorine."**
- Manganese can exhibit various oxidation states, with +7 being the highest. In this state, manganese forms stable compounds such as permanganate (MnO₄⁻) with oxygen. It also forms stable compounds with fluorine and chlorine.
- Thus, this statement is **correct**.

3. **Analyze Statement 3: "Mn³⁺ and Co³⁺ are oxidizing agents in aqueous solution."**
- Mn³⁺ can act as an oxidizing agent because it can be reduced to Mn²⁺. Similarly, Co³⁺ can also act as an oxidizing agent, being reduced to Co²⁺. Both ions can oxidize other substances while being reduced themselves.
- Therefore, this statement is **correct**.

4. **Analyze Statement 4: "Ti²⁺ and Cr²⁺ are reducing agents in aqueous solution."**
- Ti²⁺ and Cr²⁺ represent the +2 oxidation states of titanium and chromium, respectively. These ions can act as reducing agents because they can be oxidized to higher oxidation states (Ti³⁺ and Cr³⁺).
- Thus, this statement is **correct**.

### Conclusion:
After analyzing all statements, we find that the first statement, "Copper liberates hydrogen from acids," is the only incorrect statement.

### Final Answer:
The incorrect statement is **A: Copper liberates hydrogen from acids.**

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