**Core Concept**
Pneumothorax is a life-threatening condition characterized by the accumulation of air in the pleural space, leading to lung collapse. The clinical features of pneumothorax are primarily due to the displacement of the lung beneath the mediastinal structures and the loss of negative intrathoracic pressure.

**Why the Correct Answer is Right**
A pneumothorax typically presents with sudden onset of chest pain, shortness of breath, and decreased breath sounds on the affected side. The loss of lung volume can lead to mediastinal shift towards the affected side, causing tracheal deviation, and decreased venous return, resulting in tachycardia and hypotension. The accumulation of air in the pleural space can also cause increased intercostal retractions and a hyper-resonant percussion note on the affected side.

**Why Each Wrong Option is Incorrect**
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**Clinical Pearl / High-Yield Fact**
A mnemonic to remember the features of pneumothorax is "COSTS": Collapse, Oxygenation, Shock, Tachycardia, and Tracheal deviation. This helps in recalling the key clinical features of pneumothorax.

**Correct Answer:**
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