The Earth is struck by about 100 lightning bolts per second.
Why it is true
It is estimated that about 100 lightning bolts occur per second across the planet, which adds up to about 8 million per day and about 3 billion per year. Most occur over the oceans and in tropical regions.
Source: NOAA
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.