**Core Concept**
Fine-needle aspiration cytology (FNAC) is a diagnostic procedure where a thin needle is used to collect cells from a lump or mass for histopathological examination. The size of the needle used in FNAC depends on the location and accessibility of the lesion.

**Why the Correct Answer is Right**
The size of the needle required for FNAC varies based on the site and depth of the lesion. Generally, a 22-25 gauge needle is used for most FNAC procedures. The smaller gauge needle (smaller diameter) is used for superficial lesions, while a larger gauge needle (larger diameter) is used for deeper or more inaccessible lesions. A 25 gauge needle is often preferred for FNAC of thyroid nodules, lymph nodes, and breast lesions.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because a 16 gauge needle is too large for FNAC and may cause significant trauma to the surrounding tissue.
* **Option B:** This option is incorrect because a 30 gauge needle is too small and may not provide sufficient sample for histopathological examination.
* **Option C:** This option is incorrect because a 20 gauge needle is too large for superficial lesions and may cause unnecessary trauma.

**Clinical Pearl / High-Yield Fact**
When performing FNAC, it is essential to use the smallest gauge needle possible to minimize trauma to the surrounding tissue while still obtaining an adequate sample for histopathological examination.

**Correct Answer:** C. A 20-gauge needle is too large for FNAC and a 16-gauge needle is too large for any procedure, and 30 gauge is too small.