"I understood that the world was nothing" is a very melancholic or hopeless way of seeing the world.
"a mechanical chaos of casual, brute enmity" is a phrase that keeps this feeling of hopelessness; since, after all, it's all chaos.
"on which we stupidly impose our hopes and fears" is how it ends, by adding even more hopelessness to the thought, since what we wish to achieve is pure stupidity in the chaos of the world.
Which brings us to the correct answer:
D. The word choice conveys a negative and hopeless view of the world