What correctly describes the formation of lightning?

The formation of lightning is best described by the phenomenon of charging within thunderclouds, which makes "thunderclouds change their charge" the correct answer. During a storm, the movement of air and water droplets within a thundercloud leads to the separation of electrical charges. This results in the accumulation of positive and negative charges at different locations within the cloud. The potential difference between these charges can become so great that it overcomes the resistance of the air, resulting in a rapid discharge of electricity—this is observed as lightning.

The other options do not accurately reflect the nature of lightning. The assertion that lightning is purely a magnetic phenomenon neglects the key role of electrical charge separation and discharge. Claiming that lightning can only form after rain has begun fails to consider that lightning can occur even before significant precipitation falls, as the electrical processes can begin in the cloud long before raindrops are visible. Lastly, the idea that lightning requires contact with the ground is misleading; while lightning often strikes the ground, it can also occur between different parts of a cloud or between clouds, illustrating that direct ground contact is not a requirement for its formation.