**Core Concept:** The symptoms mentioned are indicative of a lesion affecting the sensory nerves that carry pain, temperature, and proprioception information. These nerves are part of the peripheral nervous system and are responsible for transmitting sensory information from the body to the central nervous system. In this question, we are looking for the location of the lesion that would cause the described symptoms.

**Why the Correct Answer is Right:** The correct answer, option C, relates to the lesion affecting the trigeminal nerve, which is responsible for carrying sensory information to the brain from the face. This nerve is divided into three divisions: the ophthalmic, maxillary, and mandibular divisions. The loss of pain and temperature sensation over the left side of the face corresponds to the involvement of the maxillary division of the trigeminal nerve.

**Why Each Wrong Option is Incorrect:**

A. This option refers to a lesion affecting the facial nerve, which is responsible for motor function and facial expression, not sensory function. The loss of pain and temperature sensation is not associated with facial nerve involvement.

B. The lesion affecting the posterior spinal cord would result in sensory loss involving the entire body, not just the face and right arm/leg. The described symptoms are not consistent with a posterior spinal cord lesion.

D. The lesion affecting the brachial plexus would result in sensory loss in the upper extremities, not the right arm and leg. The described symptoms are not consistent with a brachial plexus lesion.

**Clinical Pearl:** The correct answer, option C, emphasizes the importance of considering specific nerve divisions within the trigeminal nerve when evaluating sensory deficits. A thorough examination of a patient presenting with sensory deficits should involve assessing the dermatomes and regions supplied by specific nerves, such as the maxillary division of the trigeminal nerve in this case. This approach helps to narrow down the possible locations of the lesion and guide further diagnostic and therapeutic decisions.