"Lightning is seen before thunder is heard" is correct about thunderstorms
Step-by-step explanation:
A "thunderstorm" is a disturbance in weather that is related with lightning, dense clouds, heavy rain, hail or thunder. During a thunderstorm, lightning is always seen before thunder because the speed at which the light travels is faster than that of sound's speed.
Also, thunder's noise could be heard up to 10 km away from lightning flash. The thunder sound lasts for a few seconds. The thunder makes noise because of the rapid and fast expansion of the heating of the air.