What is the primary cause of lightning during thunderstorms?

The primary cause of lightning during thunderstorms is the buildup of static electricity, which occurs due to the movement of particles within the storm clouds. As water droplets and ice particles collide within the cloud, they can generate a separation of electrical charges. This charge separation creates an electric field. When the electric potential between areas of differing charge becomes sufficiently large, a discharge occurs in the form of lightning.

The incorrect choice highlights that friction between updrafts and downdrafts contributes to the overall dynamics of the storm but is not the sole or primary factor causing lightning. Other incorrect options, like heat exchange in clouds and temperature differences between layers, involve different atmospheric processes and do not directly account for the electrical phenomena responsible for lightning. Understanding this dynamic of charge separation is essential for comprehending how lightning is generated in thunderstorms.