Scientists might predict the following outcomes due to solar flares:
1. **Electrical systems in satellites will fail.**
2. **Radio navigation systems and global positioning systems will be inaccurate.**
3. **High-frequency radio waves used for radio communication will be blocked.**
4. **Power grid operations will go offline.**
All of the provided responses are potential impacts of solar flares, but if you need to select just one or the most direct response, "high-frequency radio waves used for radio communication will be blocked" is a common and immediate effect observed during solar flare events.