Euchlorine is:

Answer

To solve the question "Euchlorine is:", we need to understand the chemical process involved in its formation and the components that make up this mixture.

### Step-by-Step Solution:

1. **Identify the Reaction**:
- When potassium chlorate (KClO3) is heated with concentrated hydrochloric acid (HCl), a chemical reaction occurs.

2. **Understand the Products**:
- The heating of KClO3 with concentrated HCl produces a mixture of gases, primarily chlorine (Cl2) and chlorine dioxide (Cl2O).

3. **Define Euchlorine**:
- The term "Euchlorine" refers specifically to this mixture of chlorine gas (Cl2) and chlorine dioxide (Cl2O).

4. **Conclusion**:
- Therefore, we can conclude that Euchlorine is a mixture of chlorine (Cl2) and chlorine dioxide (Cl2O).

### Final Answer:
Euchlorine is a mixture of chlorine (Cl2) and chlorine dioxide (Cl2O).