**Core Concept:** The Glasgow Coma Scale (GCS) is a widely used scoring system to assess the level of consciousness in patients with trauma or neurological disorders. It comprises three components: eye opening, verbal response, and motor response. A higher score indicates better neurological function.

**Why the Correct Answer is Right:** In the given scenario, the patient's GCS can be calculated as follows:

1. Eye opening: The patient opens his eye for painful stimuli on sternum, indicating a score of 4 (since it's a painful stimulus response, not spontaneous).
2. Verbal response: The patient is able to localize to the right side, which is not mentioned in the options, but we can consider it a verbal response of "right" (score 4).
3. Motor response: The patient can flex on the left side, indicating a score of 4.

Adding these scores together, we get GCS = 4 + 4 + 4 = 12.

**Why Each Wrong Option is Incorrect:**

A. The patient's ability to localize to the right side and open eye for sternal pain is not mentioned in this option.
B. The patient's motor response (flexion on the left side) is not mentioned in this option.
C. The patient's verbal response ("right") is not mentioned in this option.
D. The patient's eye opening for painful stimuli on sternum is not mentioned in this option.

**Core Concept (repeated for clarity):** The Glasgow Coma Scale (GCS) is a scoring system used to assess a patient's level of consciousness. It comprises three components: Eye opening, Verbal response, and Motor response. A higher score indicates better neurological function.

**Why the Correct Answer is Right:** Based on the given information, the patient's GCS score is 12, indicating a good prognosis and stable neurological condition.

**Why Each Wrong Option is Incorrect:**

A. The patient's ability to localize to the right side and open eye for sternal pain is not mentioned in this option.
B. The patient's motor response (flexion on the left side) is not mentioned in this option.
C. The patient's verbal response ("right") is not mentioned in this option.
D. The patient's eye opening for painful stimuli on sternum is not mentioned in this option.

**Core Concept (repeated for clarity):** A higher GCS score indicates better neurological function and prognosis. In this case, a GCS score of 12 suggests a good prognosis and stable neurological condition.