For proper hand hygiene, it is recommended that hands be thoroughly washed for at least 15 seconds to ensure the removal of dirt, germs, and harmful bacteria.
Step 1: Analyze the options.
- (A) 10 seconds: While washing hands for 10 seconds is beneficial, it may not be sufficient for thorough cleaning.
- (B) 15 seconds: This is the correct recommendation as it allows sufficient time for proper handwashing.
- (C) 25 seconds: While longer washing may be effective, 25 seconds is not the universally recommended time.
- (D) 20 seconds: Although this time is acceptable, 15 seconds is widely acknowledged as the most common recommendation.
Step 2: Conclusion.
The correct answer is (B) 15 seconds, as it is the optimal time for handwashing according to health guidelines.
Final Answer:
\[
\boxed{(B) \, \text{15 seconds}}
\]