**Core Concept**
The pudendal nerve block is a regional anesthesia technique used to anesthetize the perineal area, including the external genitalia, perineum, and lower anal canal. It involves blocking the pudendal nerve, which provides sensory and motor innervation to these regions.

**Why the Correct Answer is Right**
The pudendal nerve arises from the S2-S4 nerve roots, which are part of the sacral plexus. The pudendal nerve carries fibers from these nerve roots to the external genitalia, perineum, and lower anal canal. Blocking the pudendal nerve disrupts the sensory and motor function of these areas, providing effective anesthesia for procedures such as circumcision, episiotomy repair, and hemorrhoidectomy.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the obturator nerve is responsible for innervating the adductor muscles of the thigh and does not contribute to the pudendal nerve.

**Option B:** This option is incorrect because the sciatic nerve is a large nerve that arises from the L4-S3 nerve roots and primarily innervates the lower limb, including the muscles of the posterior thigh and the foot.

**Option C:** This option is incorrect because the femoral nerve is responsible for innervating the muscles of the anterior thigh and the skin of the anterior thigh and leg, but it does not contribute to the pudendal nerve.

**Option D:** This option is incorrect because the ilioinguinal nerve is responsible for innervating the skin of the upper medial thigh and the root of the penis or labia majora, but it does not contribute to the pudendal nerve.

**Clinical Pearl / High-Yield Fact**
The pudendal nerve block is often performed using a single injection of local anesthetic into the pudendal canal, which is located near the ischial spine. This block provides effective anesthesia for procedures in the perineal area, but it does not affect the motor function of the muscles of the pelvic floor.

**Correct Answer: S2-S4. Nerve roots blocked in pudendal nerve block.**