Change one word from the options given below which means “that which cannot be seen through”

The correct answer is A) Opaque. An opaque object does not let light or sight pass through it, so it cannot be seen through. This is a one-word substitution item, where you pick the single word that carries the given meaning.

• Transparent (B) is the exact opposite. A transparent object allows you to see through it, like clear glass.
• Lucid (C) means clear and easy to understand, usually said of writing, speech or explanations. It has nothing to do with physical visibility.
• Unseen (D) means not seen or not noticed. It describes something that is not currently visible, but it does not say that the thing blocks vision. A thing can be unseen and still be seen through.

The core concept here is precise vocabulary: many words sound similar in meaning but differ in the property they describe. In the English paper and in precis and comprehension questions, this precision decides your marks. Mains essay and answer writing also reward it, because vague word choice weakens an argument.

Trap: Aspirants often pick Unseen because it feels like the closest match to 'cannot be seen'. Check whether the word describes the object's property (opaque) or just its state of being noticed (unseen).