Step 1: Concept Identification: The query pertains to the Demographic Transition Model, which outlines population changes from high birth/death rates to low birth/death rates during a nation's development. "Population explosion" signifies a period of exceptionally swift population increase.
Step 2: Detailed Elaboration: The demographic transition stages are: Stage 1 (Pre-industrial): High birth and death rates result in slow, stable population growth.
Stage 2 (Early industrial): Death rates decrease sharply due to advances in public health, sanitation, and food availability, while birth rates remain elevated. The significant disparity between high births and low deaths causes rapid population growth, termed the "population explosion."
Stage 3 (Late industrial): Birth rates start to fall because of increased education, urbanization, and contraception access, leading to a slower population growth rate.
Stage 4 (Post-industrial/Developed): Both birth and death rates are low, resulting in a stable or declining population.
Step 3: Conclusive Answer: The population explosion occurs during the second stage of the demographic transition, characterized by declining death rates preceding a decrease in birth rates.