Which of the following statements is not true?

Options

A. In a chemical reaction, oxidation is always accompanied by reduction.
B. When a negative ion changes to neutral species, the process is oxidation,
C. Oxidising agent has a tendency to lose electrons.
D. Conversion of `MnO_(4)^(2-)` to `MnO_(4)^(-)` is oxidation.

Explanation

To determine which of the following statements is not true, we will analyze each statement provided in the question.

### Step-by-Step Solution:

1. **Understanding Oxidation and Reduction**:
- Oxidation is the process where an atom, ion, or molecule loses electrons, resulting in an increase in oxidation state.
- Reduction is the process where an atom, ion, or molecule gains electrons, resulting in a decrease in oxidation state.

2. **Analyzing Statement A**:
- **Statement A**: "Chemical reaction oxidation is always accompanied by reduction."
- This statement is true. In any redox reaction, oxidation and reduction occur simultaneously. When one species is oxidized (loses electrons), another species must be reduced (gains those electrons).

3. **Analyzing Statement B**:
- **Statement B**: "When a negative ion changes into a neutral species, the process is oxidation."
- This statement is also true. For example, when a chloride ion (Cl⁻) loses an electron to become a neutral chlorine atom (Cl), it is undergoing oxidation because its oxidation state increases from -1 to 0.

4. **Analyzing Statement C**:
- **Statement C**: "An oxidizing agent has a tendency to lose electrons."
- This statement is false. An oxidizing agent is a substance that gains electrons (is reduced) in a chemical reaction while causing another substance to be oxidized. Therefore, it does not lose electrons; it gains them.

5. **Analyzing Statement D**:
- **Statement D**: "The oxidation state of manganese changes from +6 to +7 in a reaction."
- This statement is true. If the oxidation state of manganese increases from +6 to +7, it indicates that manganese is being oxidized, which is a correct interpretation of the change in oxidation state.

### Conclusion:
- The statement that is not true is **Statement C**: "An oxidizing agent has a tendency to lose electrons."