Step 1: Why does moisture content matter for hard gelatin capsules?
Gelatin is a protein that is sensitive to moisture. Too little moisture makes the shells brittle and cracking occurs during filling. Too much moisture makes them soft, sticky, and prone to deformation.
Step 2: The standard moisture range.
Hard gelatin capsule shells are maintained at 13–16% moisture content as per pharmacopoeial standards (IP/BP/USP). This range gives them the right flexibility and mechanical strength.
Step 3: Eliminate the wrong options.
20–25% is far too high; the shells would become limp and stick together. 1–2% is far too low; the shells would be extremely brittle and shatter on handling. 5–8% is below the acceptable range and would still result in fragile capsules.
Step 4: Storage implication.
Because of this moisture requirement, hard gelatin capsules must be stored at controlled humidity (35–65% RH). In very dry or very humid environments, the capsule properties degrade.
Step 5: Conclusion.
The pharmacopoeially specified moisture content for hard gelatin capsule shells is 13–16%, not higher or lower.
Answer: Option (4) — 13–16%