The chandra x-ray observatory must operate in space because:

a) x rays are too dangerous to be allowed on the ground.
b) x rays do not penetrate earth's atmosphere.
c) x-ray telescopes require the use of grazing incidence mirrors.
d) it was built by nasa.

B) X rays do not penetrate Earth's atmosphere

Explanation:

The Chandra X-Ray observatory should operate in space due to the nature of the radiation it is using. X-rays are high energy electromagnetic radiations. The observatory will not be able to function properly since it uses x-ray because, the rays cannot penetrate the earth's atmosphere. A radiation of this type would easily be cut off by the particles in the atmosphere. The observatory has to be positioned outside of the earth.  

iii. and iv. only is the right answer