**Core Concept**
Cardiac tamponade and tension pneumothorax are two life-threatening conditions that require prompt differentiation in emergency settings. Cardiac tamponade occurs when fluid accumulates in the pericardial sac, compressing the heart and impeding its function. Tension pneumothorax occurs when air enters the pleural space and pressure builds up, causing the lung to collapse and shift the mediastinum.

**Why the Correct Answer is Right**
Differentiation between these two conditions is crucial, as their management strategies differ significantly. The correct answer is **Point-of-Care Ultrasound (POCUS)**, particularly the focused assessment with sonography for trauma (FAST) exam. POCUS allows for rapid assessment of cardiac and thoracic structures, enabling the identification of the characteristic 'collapsing lung sign' in tension pneumothorax, which is not seen in cardiac tamponade. This sign is indicative of the lung's inability to expand due to the increasing intrathoracic pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** Chest X-ray is often used in the initial assessment of trauma patients but is not sufficient for differentiating between cardiac tamponade and tension pneumothorax due to its limited sensitivity and specificity. It may show signs of both conditions but cannot reliably distinguish between them.
**Option B:** Electrocardiogram (ECG) changes can be seen in both conditions, such as low voltage and electrical alternans in cardiac tamponade, and electrical alternans and widened QRS complex in tension pneumothorax. However, ECG findings are non-specific and cannot reliably differentiate between these two conditions.
**Option C:** Clinical examination, including physical signs such as pulsus paradoxus, jugular venous distension, and decreased breath sounds, can suggest the presence of either condition but is not sufficient for definitive diagnosis.

**Clinical Pearl / High-Yield Fact**
In a trauma patient with suspected cardiac tamponade or tension pneumothorax, POCUS should be performed immediately, as it can guide emergency thoracocentesis or pericardiocentesis if necessary.

**Correct Answer:** C.