**Core Concept**
Air blast injury, also known as primary blast injury, occurs when a shockwave generated by an explosion reaches the body and causes damage to internal organs. This type of injury is often seen in military and industrial settings.

**Why the Correct Answer is Right**
The most common organ involved in air blast injury is the lung. When the shockwave from an explosion reaches the body, it can cause the air pressure in the lungs to increase rapidly, leading to alveolar rupture and hemorrhage. This is due to the lung's unique structure, which consists of delicate alveoli that are easily damaged by rapid changes in air pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** The heart is not the most common organ involved in air blast injury, although it can be affected. The heart is more resistant to the effects of shockwaves due to its robust structure and surrounding mediastinal tissues.
**Option B:** The liver is not typically involved in air blast injury, as it is relatively protected by the ribcage and abdominal muscles.
**Option C:** The kidneys are not commonly affected by air blast injury, as they are not directly exposed to the shockwave.

**Clinical Pearl / High-Yield Fact**
In air blast injury, the severity of lung damage is often correlated with the intensity of the shockwave and the duration of exposure. This is why blast injuries can be particularly devastating in enclosed spaces, where the shockwave is amplified and prolonged.

**Correct Answer:** C. The lung is the most common organ involved in air blast injury.