Phenol coefficient calculation: A 1:600 dilution of a test compound kills a standard Staphylococcus aureus population in 10 minutes (but not 5 minutes). A 1:60 dilution of phenol achieves the same kill time. What is the phenol coefficient of the test compound?

Introduction: The phenol coefficient compares the disinfecting power of a test agent to phenol under standardized conditions. It is a ratio of effective dilutions producing the same kill in the same time.

Given Data / Assumptions:

• Test compound effective dilution (10 min kill): 1:600.
• Phenol effective dilution (10 min kill): 1:60.
• Same organism, temperature, and exposure time.

Concept / Approach: Phenol coefficient = (dilution of test agent that is effective) / (dilution of phenol that is effective). Use the highest dilution (greatest number) that produces the specified effect in the specified time for both agents.

Step-by-Step Solution: Write the ratio using effective dilutions. PC = (600) / (60). Compute: 600 / 60 = 10. Therefore the test agent is 10× as effective as phenol by this metric.

Verification / Alternative check: If the time requirement changed (e.g., 5 minutes), you would use the corresponding effective dilutions for both substances; here only the 10-minute result qualifies for both, so the ratio is unambiguous.

Why Other Options Are Wrong: 1, 5, 50, 100 – do not match the computed ratio 600/60.

Common Pitfalls: Inverting the ratio (phenol/test) or using non-comparable times, which gives the wrong coefficient.

Final Answer: 10.