**Core Concept**
Kennedy's classification is a system used in prosthodontics to categorize partially edentulous arches based on the location and extent of tooth loss. It helps in designing and fabricating dental prostheses. The classification is primarily based on the relationship between the remaining teeth and the edentulous spaces in both the maxillary and mandibular arches.

**Why the Correct Answer is Right**
A Class III mandibular arch in Kennedy's classification refers to a partially edentulous arch where there are teeth on both sides of the edentulous space, with the edentulous space located posterior to the remaining teeth. This classification is relevant in cases where a bilateral edentulous area is present, and there is at least one natural tooth on each side of the edentulous space. The correct classification of a Class III mandibular arch is essential for determining the optimal design and fabrication of a dental prosthesis.

**Why Each Wrong Option is Incorrect**
**Option A:** A Class III maxillary arch would have a unilateral edentulous space, which does not match the description provided in the question.

**Option C:** A Class II mandibular arch would have a unilateral edentulous space with a posterior abutment, which is not the same as a Class III mandibular arch.

**Option D:** A Class IV mandibular arch would have a unilateral edentulous space with a distal extension, which does not match the description provided in the question.

**Clinical Pearl / High-Yield Fact**
Kennedy's classification is a crucial tool for prosthodontists to determine the optimal design and fabrication of dental prostheses. Understanding the different classes of partially edentulous arches is essential for achieving successful outcomes in dental rehabilitation.

✓ Correct Answer: B. Class III mandibular arch