**Core Concept**
The determination of death due to drowning involves identifying specific signs and changes in the body that confirm the cause of death. In forensic pathology, the diagnosis of drowning requires a thorough examination of the body, including the lungs, airways, and other organs.

**Why the Correct Answer is Right**
The correct answer is **C. Pulmonary edema with blood in the alveoli and bronchi**. This condition occurs when water enters the lungs and causes fluid to accumulate in the alveoli, leading to a characteristic appearance of blood-tinged froth in the airways. The presence of blood in the alveoli and bronchi is a definitive sign of drowning, as it indicates that water entered the lungs and caused damage to the delicate alveolar structures.

**Why Each Wrong Option is Incorrect**
**Option A:** **Rigor mortis** is a post-mortem change that occurs in the body after death, but it is not specific to drowning and can occur in any case of death.

**Option B:** **Submersion in water** is a necessary condition for drowning, but it is not a definitive sign of death due to drowning. Many people can survive submersion in water without experiencing any of the characteristic changes associated with drowning.

**Option D:** **Electrolyte imbalance** can occur in cases of drowning, but it is not a definitive sign of death due to drowning. Electrolyte imbalances can occur in many other conditions, and they do not provide specific evidence of drowning.

**Clinical Pearl / High-Yield Fact**
When investigating a case of suspected drowning, it is essential to look for the presence of blood in the alveoli and bronchi, as this is a definitive sign of drowning. The absence of blood in these areas does not rule out drowning, but the presence of blood is highly suggestive of this cause of death.

**Correct Answer:** C. Pulmonary edema with blood in the alveoli and bronchi.