*Question T3B04:
What is the velocity of a radio wave traveling through free space?*  

*Correct Answer is  A: Speed of light*  

### AI Response: (may contain errors)  

The correct answer to the question about the velocity of a radio wave traveling through free space is:

**Speed of light**

### Explanation:

1. **Why the correct answer is correct:**
   - Radio waves, like all electromagnetic waves, travel at the speed of light in a vacuum. This speed is approximately $299,792,458$ meters per second (or about $300,000$ km/s). In free space, the speed of light is constant and does not depend on the frequency or wavelength of the wave.

2. **Why the other choices are incorrect:**
   - **B: Speed of sound**  
     - The speed of sound is much slower than the speed of light and depends on the medium through which it travels (e.g., air, water). It is not applicable to radio waves, which are electromagnetic and do not require a medium.
   
   - **C: Speed inversely proportional to its wavelength**  
     - While the speed of a wave can be related to its wavelength and frequency, in free space, the speed of light is constant. The relationship between speed ($v$), frequency ($f$), and wavelength ($\lambda$) is given by the formula:  
     $$v = f \times \lambda$$  
     - Here, $v$ is the speed of light, which does not change with wavelength in free space.
   
   - **D: Speed that increases as the frequency increases**  
     - This statement is incorrect because the speed of light remains constant regardless of frequency. While frequency and wavelength are inversely related, the speed of light does not change with frequency.

### Useful Formulas:
- The relationship between speed, frequency, and wavelength is crucial:
  $$v = f \times \lambda$$  
  where:
  - $v$ = speed of the wave (in free space, this is the speed of light)
  - $f$ = frequency (in hertz)
  - $\lambda$ = wavelength (in meters)

This formula helps understand how frequency and wavelength relate, but remember that in free space, the speed of light is always constant.