**Core Concept**
Emphysema is a type of chronic obstructive pulmonary disease (COPD) characterized by destruction of alveolar walls and enlargement of air spaces, leading to impaired gas exchange and lung function. This results in a reduction in lung volumes, particularly vital capacity and diffusing capacity, as well as an increase in residual volume.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiological changes in emphysema. In emphysema, the destruction of alveolar walls leads to an increase in residual volume due to air trapping, a decrease in vital capacity due to the loss of elastic recoil, and a decrease in diffusing capacity due to the destruction of alveolar-capillary membrane. This results in a decrease in the forced expiratory volume in one second (FEV1) and a decrease in the forced vital capacity (FVC) ratio.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the FEV1/FVC ratio is actually decreased in emphysema, not increased.
**Option B:** This option is incorrect because the residual volume is actually increased in emphysema, not decreased.
**Option C:** This option is incorrect because the diffusing capacity is actually decreased in emphysema, not increased.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of emphysema is the use of accessory muscles for breathing, such as the sternocleidomastoid and scalene muscles, due to the loss of elastic recoil and increased airway resistance.

**Correct Answer:** C.