Which of the following is an important safety rule when cleaning any firearm?

Wearing eye and hand protection is crucial when cleaning any firearm because it helps safeguard against potential injuries. During the cleaning process, there may be the risk of small particles, solvents, or other materials that could irritate the skin or eyes. Protective gear, such as safety glasses and gloves, ensures that the person cleaning the firearm remains safe from these hazards.

The other options present practices that wouldn't ensure safety effectively. Keeping a firearm loaded, for instance, poses a significant risk of accidental discharge, while using only water and soap might not be effective for all types of firearms or the specific contaminants involved. Additionally, cleaning during a thunderstorm is not inherently dangerous to the act of cleaning a firearm itself, therefore it doesn't provide a relevant safety guideline. Overall, wearing proper protection is a fundamental safety measure that should always be prioritized in firearm maintenance activities.