Question

What causes lightning during a thunderstorm ?

Answer 1

There are electric charges collected on the clouds and in the atmosphere due to various reactions and sun light radiation and greenhouse gases.

The charges are brought closer to each other and when the potential of static charges reaches very very high value like millions of volts. Then the breakdown voltage of air /atmosphere is exceeded.  So electric discharge takes place. During a thunderstorm the conditions are exaggerated , so the lightning happens at that time. 

Answer 2

Question

What causes lightning during a thunderstorm ?

Answer

A thunderstorm is a disturbance in whether that consists of heavy rains lightning strong winds dense clouds affect it occur in hot humid and tropical areas consisting of coastal region.