In the Hench scale test, the proper Polyphosphate dose is the lowest dose that delays noticeable discoloration for a period of how many days?

• A. 2 days
• B. 3 days
• C. 4 days
• D. 5 days

Answer: (C)

The Hench scale test is about finding the smallest polyphosphate dose that keeps water from discoloring for a defined period. You test increasing doses and watch how long the water stays clear before discoloration appears. The dose that first achieves the required duration is considered the proper dose.

In this question, the required duration is four days. So the proper dose is the lowest dose that delays noticeable discoloration for four days. Four days is chosen as the endpoint because it provides sufficient aesthetic protection without overspending on chemical dose. Doses that only delay discoloration for shorter periods (two or three days) don’t meet the goal, while a dose that delays for longer (five days) isn’t the minimal amount needed to reach the four-day target.