*Question E3C08:
Which of the following is the space-weather term for an extreme geomagnetic storm?*  

*Correct Answer is  D: G5*  

### AI Response: (may contain errors)  

The correct answer to the question about the space-weather term for an extreme geomagnetic storm is **G5**.

### Explanation of the Correct Answer:
- **G5** is the classification used by the NOAA Space Weather Prediction Center to denote an extreme geomagnetic storm. The G-scale ranges from G1 (minor) to G5 (extreme), with G5 indicating the highest level of geomagnetic activity, which can cause significant disruptions to power systems, satellites, and radio communications.

### Why the Other Choices are Incorrect:
- **A: B9**: This designation is not related to geomagnetic storms. It is often used in the context of solar flares, where B-class flares are relatively weak.
  
- **B: X5**: While X-class flares are the most powerful type of solar flares, the number (5 in this case) indicates the strength of the flare, not a geomagnetic storm classification. An X5 flare can lead to geomagnetic storms, but it is not a direct classification of the storm itself.

- **C: M9**: Similar to B9, M-class flares are moderate in strength. An M9 flare is significant but does not correspond to the G-scale for geomagnetic storms.

### Summary:
- The G-scale is specifically used for geomagnetic storms, with G5 being the highest level.
- The other options (B9, X5, M9) refer to solar flares and do not classify geomagnetic storms.

This understanding of the classifications is crucial for recognizing the impact of solar activity on Earth and preparing for potential disruptions in communication and power systems.