In this sentence completion question, you must choose the word that best completes the following sentence so that it is meaningful and grammatically correct: "The airline was unable to give us a reason for the ______________ departure delay." Which option correctly describes a delay for which no clear reason can be given?

Introduction / Context:
This question checks your understanding of adjectives that describe the nature of an event, particularly when there is or is not a clear explanation. The sentence is about an airline that cannot provide a reason for a departure delay. The correct word must convey that the delay cannot be explained, not that it cannot be seen, divided or defeated. Vocabulary precision is important in competitive examinations because similar sounding words often have very different meanings.

Given Data / Assumptions:

• The sentence is: The airline was unable to give us a reason for the ______________ departure delay.
• The airline cannot give a reason, so the delay lacks a clear explanation.
• The options are indivisible, invincible, invisible and inexplicable.
• The correct word needs to describe something that cannot be explained.

Concept / Approach:
The key is to match the context give a reason for with a word that semantically fits. In English, when no explanation is possible, we say something is inexplicable. Indivisible means not able to be divided, invincible means too powerful to be defeated, and invisible means not able to be seen. Only inexplicable directly describes an event that defies explanation. By aligning meaning with the phrase give us a reason for, you can easily eliminate the other options.

Step-by-Step Solution:
Step 1: Focus on the main idea. The airline was unable to give us a reason indicates that the delay cannot be explained satisfactorily. Step 2: Recall that the word inexplicable means impossible or very difficult to explain. Step 3: Insert inexplicable into the sentence: The airline was unable to give us a reason for the inexplicable departure delay. This sounds natural and accurately describes a delay with no clear cause. Step 4: Test indivisible. It means not able to be divided, which relates to mathematics or unity, not to delays or reasons. Step 5: Test invincible and invisible. Invincible relates to strength in battle or competition, and invisible relates to sight, neither of which connect to reasons or explanations for a delay. Therefore they are not suitable.

Verification / Alternative check:
Good exam technique involves paraphrasing the sentence. You could say The airline was unable to give us a reason for the delay, which seemed impossible to explain. The phrase impossible to explain is almost a direct definition of inexplicable. This confirms that inexplicable is the only option that correctly captures the idea. Reading the sentence aloud with each alternative further shows that only inexplicable creates a coherent and natural expression in standard English usage.

Why Other Options Are Wrong:
Indivisible is typically used in contexts like indivisible by two, or an indivisible nation, and refers to something that cannot be separated into parts. It does not describe a delay. Invincible is often used for warriors, teams or forces that cannot be defeated, as in an invincible army, and has nothing to do with reasons or explanations. Invisible refers to something that cannot be seen, such as invisible ink or an invisible object, which again does not fit the context of a departure delay that lacks an explanation. None of these words pair well with the phrase reason for the delay.

Common Pitfalls:
Students sometimes confuse words that share similar prefixes like in or im and assume that their meanings are interchangeable. However, English vocabulary is full of such false friends, and each word must be understood independently. Another common pitfall is rushing through the options and focusing only on sound rather than meaning. Because these are all formal sounding words, it is important to connect each one to a simple definition in your mind before making a choice. Slowing down for a moment to recall meanings can greatly improve accuracy in vocabulary questions.

Final Answer:
A delay for which no clear reason can be given is best described as an inexplicable departure delay.