**Core Concept**
The offset angle of a dental instrument, specifically the Gracey curette, is a critical design feature that affects its usability and effectiveness in removing subgingival calculus and plaque. The offset angle is the angle between the blade and the shank of the instrument, which influences the instrument's ability to access and clean areas between teeth.

**Why the Correct Answer is Right**
The Gracey curette has a distinctive offset angle of 8 degrees, which allows it to easily access and clean areas between teeth. This design feature enables the instrument to effectively remove subgingival calculus and plaque, making it a valuable tool in periodontal therapy. The offset angle also helps to reduce the risk of instrument breakage and improves the overall efficiency of the procedure.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not match the actual offset angle of the Gracey curette.
**Option B:** This option is incorrect because it is not a recognized design feature of the Gracey curette.
**Option C:** This option is incorrect because it is not the correct offset angle of the Gracey curette.

**Clinical Pearl / High-Yield Fact**
It is essential to choose the correct instrument for each specific periodontal procedure to ensure effectiveness and safety. The Gracey curette is particularly useful for removing subgingival calculus and plaque, but it must be used with the correct offset angle to avoid damaging the surrounding tissues.

**Correct Answer: C. 8 degrees**