Select the correct option:
The professor’s remarks were so dense with jargon that they bordered on __________.

Correct option is A

The correct option to fill in the blank is (a) opacity.
The phrase “bordered on” is followed by a noun, and the meaning required is lack of clarity or understandability. Opacity means the quality of being difficult to understand; obscurity (also: not letting light pass through). (Hindi meaning: अस्पष्टता/दुरूहता)
Example: The legal document’s opacity confused even experienced readers.
Explain why other options are incorrect:
· (b) opaque: adjective form; after “bordered on” we need a noun here.
· (c) opacus: incorrect/irrelevant word for this context.
· (d) opalescent: means showing shifting colours like opal; unrelated to meaning.
Information booster:
· Common collocation: border on + noun (border on insanity, border on rudeness, border on chaos).