Answer :
since the star is 100 light years away, the distance the light would need to reach earth is so huge and time needed will be so big. Above these, the light may get scattered while travelling such a huge distance
As it is told in the question the star is 100 light years away,so,if it explodes today we would be able to see the explosion but after 100 years from the explosion as light would take 100 years to reach to the Earth.