Step 1: Understanding the Question:
The question gives a Carr's compressibility index of 12-16 for a powder and asks what flowability rating that corresponds to.
Step 2: Key Formula or Approach:
Carr's index compares the bulk density (loosely poured powder) with the tapped density (powder after settling by tapping):
\[ \text{CCI} = \frac{\rho_{tapped} - \rho_{bulk}}{\rho_{tapped}} \times 100 \]
A powder that barely changes volume on tapping has a low index and flows freely, since its particles are already packed about as tightly as they will get. A powder that settles a lot on tapping has a high index and flows poorly, since the particles were loosely arranged and rearrange easily under vibration.
Step 3: Detailed Explanation:
Pharmacopeial flow tables map index values to descriptive ratings: 1-10 excellent, 11-15 good, 16-20 fair, 21-25 passable, and above that, poor to very poor. A value of 12-16 mostly falls in the good band (11-15), just touching the edge of fair. Practically, powders in this range are considered flowable enough for direct compression or capsule filling with standard equipment, though a formulator would still keep an eye on this powder since it sits close to the fair and good boundary.
Step 4: Final Answer:
A Carr's compressibility index of 12-16 corresponds to good flowability.