**Core Concept**
A pneumothorax is a condition where air enters the pleural space, leading to a partial or total collapse of the lung. In this scenario, the patient has a moderate-sized pneumothorax without tension, which means there is no immediate life-threatening condition. The physical findings in such cases can be subtle and may not always be obvious.

**Why the Correct Answer is Right**
The physical examination of a patient with a moderate-sized pneumothorax may reveal decreased breath sounds over the affected area, which can be detected by auscultation. This occurs because the air in the pleural space prevents the transmission of sound waves from the lung to the stethoscope. Additionally, the patient may exhibit a trapezius ridge, which is a bulge in the intercostal space due to the air in the pleural space. The trapezius ridge is a classic sign of a pneumothorax.

**Why Each Wrong Option is Incorrect**
* **Option A:** Absence of breath sounds is not a specific finding for a pneumothorax. It can also be seen in cases of pleural effusion or atelectasis.
* **Option B:** Hyper-resonance is typically seen in cases of pneumothorax with air in the pleural space, but it is not a reliable sign in moderate-sized pneumothorax without tension.
* **Option C:** Decreased vocal fremitus can be seen in cases of pneumothorax, but it is not as specific as decreased breath sounds.
* **Option D:** No physical finding is present is incorrect because there are indeed physical findings that can be detected in a patient with a moderate-sized pneumothorax.

**Clinical Pearl / High-Yield Fact**
A key clinical pearl to remember is that a trapezius ridge is a classic sign of a pneumothorax, especially in cases where the patient is sitting up. This sign can be easily missed if the examiner is not aware of its significance.

**Correct Answer: C. Decreased breath sounds over the affected area.**