According to the USP, zinc oxide paste should contain not less than and not more than zinc oxide.

• A. 24%, 26%
• B. 20%, 24%
• C. 22%, 28%
• D. 26%, 28%

Answer: (A)

The idea being tested is how USP quality specifications regulate the amount of an active ingredient in a finished product. For zinc oxide paste, the USP sets a tight content specification for zinc oxide: not less than 24% and not more than 26%. This narrow range centers around a typical target of 25%, ensuring each gram of paste delivers a consistent amount of zinc oxide. Keeping the potency within this window is important for predictable therapeutic effect and safety; if the zinc oxide content were lower, the paste might be less effective, and if higher, it could increase irritation or cause other issues. The rest of the paste serves as the base, but the critical factor for potency and quality control is that zinc oxide falls within that 24–26% range.