A paradoxical statement happens when the elements of a statement contradict each other, but still has a comprehensible meaning. The pair of words that could be combined into one are<em> NOISE AND SILENCE (option c). </em>they are antonyms, they have opposite meaning, in the same well-formed sentence they can form a coherent statement to express a conceptual truth.
Imagery is when you describe something visually with words. In this sentence, "sharp hiss" is imagery because it makes you think of what is happening like an image.