Who was the first to discover that the sun was actually the center of the universe

Nicolaus Copernicus

Explanation:

With the development of the heliocentric model by Nicolaus Copernicus in the 16th century, the Sun was believed to be the center of the Universe, with the planets (including Earth) and stars orbiting it.

a. poison gas was sprayed over battlefields by airplanes to weaken enemy positions before major attacks.