Select the most appropriate word that can substitute the highlighted word in the given sentence without altering the sentence's meaning.
The professor’s lecture on quantum mechanics was as enlightening as it was challenging.

Correct option is B

The correct substitution of the highlighted word "enlightening" is (b) illuminating.
Explanation:
“Enlightening” means providing insight, understanding, or new information. The word "illuminating" is a near-perfect synonym as it also conveys clarity and intellectual light. Replacing "enlightening" with "illuminating" maintains the intended meaning of the sentence.
Correct sentence:
The professor’s lecture on quantum mechanics was as illuminating as it was challenging.
Meanings of all options:
· (a) Confusing – unclear, puzzling.
Hindi meaning: उलझन भरा ❌
· (b) Illuminating – enlightening, clarifying.
Hindi meaning: जानकारी देने वाला, स्पष्ट करने वाला ✅
· (c) Perplex – to confuse or puzzle (verb).
Hindi meaning: उलझन में डालना ❌
· (d) Dull – boring or lacking interest.
Hindi meaning: नीरस ❌