**Core Concept**
The principal mode of heat exchange in an infant incubator involves the removal of heat from the incubator environment to maintain a stable temperature for the infant. This process is crucial in neonatal care to prevent hypothermia, which can be life-threatening.

**Why the Correct Answer is Right**
The correct answer is **convection**. Convection is the process by which heat is transferred through the movement of fluids, in this case, air. In an infant incubator, warm air is circulated by a fan, and as it rises, it cools, creating a circulation of air that removes heat from the incubator. This process is essential in maintaining a stable temperature within the incubator.

**Why Each Wrong Option is Incorrect**
**Option A:** Radiation is a mode of heat exchange, but it is not the principal mode in an infant incubator. Radiation involves the transfer of heat through electromagnetic waves, which is not the primary mechanism in this context.

**Option B:** Conduction is a mode of heat exchange that involves direct contact between objects. While conduction does occur in an infant incubator, it is not the principal mode of heat exchange.

**Option C:** Evaporation is a mode of heat exchange that involves the transfer of heat through the process of liquid turning into vapor. While evaporation does occur in an infant incubator, it is not the principal mode of heat exchange.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the temperature in an infant incubator should be maintained within a narrow range (around 36.5°C to 37.5°C) to prevent both hypothermia and hyperthermia. This narrow temperature range is critical in preventing complications in premature infants.

**Correct Answer:** C. Convection.