**Core Concept:**
The question is asking about a reflex that is active when the mandible (jaw) is in its resting position. Reflexes are rapid, involuntary responses triggered by specific stimuli, including mechanical, thermal, or chemical stimuli. In this context, we are focusing on the trigeminal reflex, which is triggered by stimuli in the jaw area.

**Why the Correct Answer is Right:**
The correct answer, **Option C: Mandibular Reflex**, is the reflex that occurs when the mandible is in its resting position. This reflex is activated when a stimulus is applied to the jaw or masticatory muscles, causing involuntary actions such as biting, chewing, or swallowing. The mandibular reflex is part of the trigeminal reflex arc, which includes the trigeminal nerve, trigeminal sensory nucleus, and the motor nucleus within the medulla oblongata.

**Why Each Wrong Option is Incorrect:**

A. **Option A: Vagal Reflex (Cirsovagal Reflex)** - This reflex is related to the stimulation of the carotid sinus and carotid body receptors, which are not involved in the jaw movements.
B. **Option B: Glossopharyngeal Reflex (Gag Reflex)** - This reflex is triggered by stimuli in the pharynx or tonsils and is not related to jaw movements.
D. **Option D: Orofacial Reflex (Mandibular Reflex)** - This reflex is also related to jaw movements and is the correct answer among the given options.

**Clinical Pearl:**
The mandibular reflex demonstrates the interconnectedness of the trigeminal, vagal, and glossopharyngeal reflexes in the autonomic nervous system. This reflex plays a crucial role in maintaining homeostasis, protecting the airway, and enabling essential oral functions, such as chewing, swallowing, and breathing. Understanding these reflexes helps medical professionals to diagnose and treat various neurological disorders involving the oral and pharyngeal regions.