A mixture of reactants may be thermodynamically unstable but kinetically stable.

Answer

### Step-by-Step Solution:

1. **Understanding the Terms**:
- **Thermodynamic Stability**: Refers to the stability of a system based on its energy state. A system is thermodynamically unstable if it can spontaneously change to a lower energy state.
- **Kinetic Stability**: Refers to the rate at which a reaction occurs. A system is kinetically stable if the reaction does not proceed at a noticeable rate, even if it is thermodynamically favorable.

2. **Analyzing the Statement**:
- The statement claims that a mixture of reactants can be thermodynamically unstable while being kinetically stable. This means that the reactants have the potential to react and form products (thermodynamically unstable), but the reaction does not occur at a significant rate (kinetically stable).

3. **Example to Illustrate the Concept**:
- Consider a mixture of coal and oxygen.
- **Thermodynamic Perspective**: The reaction between coal and oxygen produces carbon dioxide (CO2). At equilibrium, the formation of CO2 is favored, indicating that the mixture is thermodynamically unstable as it can spontaneously react to form a more stable product.
- **Kinetic Perspective**: However, the reaction does not occur at room temperature. Coal does not ignite and react with oxygen until it reaches a certain temperature (ignition temperature). Therefore, the reaction rate is effectively zero under normal conditions, making the mixture kinetically stable.

4. **Conclusion**:
- The example of coal and oxygen illustrates that while the mixture is thermodynamically unstable (as it can lead to the formation of CO2), it remains kinetically stable due to the high activation energy barrier that prevents the reaction from occurring without sufficient heat.