Assertion If the path of a charged particle in a region of uniform electric and magnetic field is not a circle, then its kinetic energy may remain constant.
Reason In a combined electric and magnetic field region a moving charge experiences a net force
`F=qE+q(VxxB),` where symbols have their usual meanings.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that if the path of a charged particle in a uniform electric and magnetic field is not circular, then its kinetic energy may remain constant. We need to evaluate whether this statement is true or false.

2. **Understanding the Reason**: The reason provided states that in a combined electric and magnetic field, a moving charge experiences a net force given by the equation \( F = qE + q(v \times B) \). This is known as the Lorentz force.

3. **Analyzing the Forces**: The Lorentz force consists of two components:
- The electric force \( F_E = qE \)
- The magnetic force \( F_B = q(v \times B) \)

4. **Effect of Electric Field**: The presence of an electric field \( E \) exerts a force on the charged particle that causes it to accelerate. This acceleration changes the velocity of the particle.

5. **Kinetic Energy Calculation**: The kinetic energy \( K \) of a charged particle is given by:
\[ K = \frac{1}{2} mv^2 \]
If the velocity \( v \) changes due to the electric field, the kinetic energy will also change. Therefore, if the path is not circular (for example, helical), the kinetic energy cannot remain constant.

6. **Conclusion on Assertion**: Since the electric field causes acceleration and thus a change in speed, the assertion that the kinetic energy may remain constant is incorrect.

7. **Conclusion on Reason**: The reason is correct as it accurately describes the net force acting on the charged particle in the presence of both electric and magnetic fields.

8. **Final Evaluation**: Therefore, we conclude that the assertion is false, while the reason is true.

### Final Answer:
- Assertion: **False**
- Reason: **True**