Long range radio transmission is possible when the radiowaves are reflected from the ionosphere. For this to happen the frequency of the radio waves must be in the range:

Options

A. 1 - 3 MHz
B. 150 - 500 kHz
C. 8 - 25 MHz
D. 80 - 150 MHz

Answer

To determine the frequency range of radio waves that can be reflected from the ionosphere for long-range radio transmission, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Skywaves**:
- Long-range radio transmission utilizes waves that are reflected off the ionosphere. These waves are known as skywaves.

2. **Frequency Range for Skywaves**:
- The effective frequency range for skywaves is typically between 2 megahertz (MHz) and 30 megahertz (MHz). This range allows the waves to reflect off the ionosphere effectively.

3. **Evaluating the Options**:
- We need to evaluate the given options to identify which one falls within the 2 MHz to 30 MHz range.
- Option 1: 1 to 3 MHz - This range does not include 2 MHz and is therefore incorrect.
- Option 2: In kilohertz - This is also incorrect as it does not fall within the megahertz range.
- Option 3: 8 to 25 MHz - This range is within the 2 MHz to 30 MHz range and is correct.
- Option 4: 80 to 150 MHz - This range is too high and does not fall within the effective range for skywave reflection.

4. **Conclusion**:
- The correct frequency range for long-range radio transmission using skywaves is **8 to 25 MHz**.

### Final Answer:
The frequency of the radio waves must be in the range of **8 to 25 megahertz**.