Under which condition is a person at greatest risk of developing hypothermia?

Being immersed in cold water places a person at the highest risk of developing hypothermia due to the rapid loss of body heat that occurs in these conditions. Water conducts heat away from the body much more efficiently than air, making it easier to lose core temperature. Immersion in cold water can lead to hypothermia in a matter of minutes, especially if the water temperature is significantly lower than the body temperature.

In contrast, being in a warm environment, wearing multiple layers of clothing, or participating in physical activity would generally help prevent hypothermia. A warm environment provides heat that can keep the body warm, multiple layers of clothing create insulation and can trap body heat, while physical activity generates heat through metabolic processes. However, when in cold water, the body's mechanisms for retaining heat are overwhelmed, resulting in a rapid drop in core temperature.