Out of the following alternatives, choose the single word that can be used for the given description. The description is: That which cannot be believed.

Introduction / Context:
This one word substitution question tests understanding of adjectives related to belief and credibility. The description given is that which cannot be believed. English has an adjective that directly expresses this idea and is often used for things that seem too unusual, shocking, or extraordinary to be accepted easily as true. Recognising this word strengthens vocabulary for describing extreme situations, surprising events, or doubtful claims.

Given Data / Assumptions:

• Description: That which cannot be believed.
• Options: Awesome, Incredible, Credible, Ineffective.
• We assume the focus is on belief and trustworthiness, not on usefulness or emotional impact.
• The task is to select the adjective whose core meaning matches cannot be believed.

Concept / Approach:
The key concept is the difference between credible and incredible. Credible means believable or reliable, while incredible literally means not believable. Over time, incredible is also used informally to mean amazing or extraordinary, but the root meaning still connects to disbelief. Awesome describes something that inspires awe, and ineffective describes something that does not work well. The approach is to focus on the exact wording of the description cannot be believed and match it to the literal or original meaning of the options.

Step-by-Step Solution:
Step 1: Identify the central idea of the description: something is impossible or very hard to believe. Step 2: Consider Incredible. Formed from in plus credible, it literally means not believable and is used for things that are astonishing or beyond belief. Step 3: Consider Credible. This means believable or trustworthy, which is the opposite of what the description states. Step 4: Consider Awesome. While it may describe something very impressive, it does not directly mean cannot be believed. Step 5: Consider Ineffective. This refers to something that does not produce the desired result and has no connection to belief or disbelief. Step 6: Conclude that Incredible is the only option that correctly matches the phrase that which cannot be believed.

Verification / Alternative check:
To verify, consider example sentences. We might say the story he told was incredible, meaning it was so strange or unlikely that it was hard to believe. Dictionaries define incredible as so extraordinary as to seem impossible or not to be believed. In contrast, credible evidence means evidence that can be trusted and believed. Awesome is often used to praise things as wonderful or impressive, for example, an awesome performance, but this is different from the idea of not believable. Ineffective is used in contexts like an ineffective treatment and does not refer to belief at all. These comparisons confirm that incredible is the correct choice.

Why Other Options Are Wrong:
Awesome: Focuses on emotional impact and sense of awe rather than belief or disbelief.
Credible: Means believable or reliable, which is the direct opposite of cannot be believed.
Ineffective: Describes something that fails to produce results and is unrelated to the concept of believability.

Common Pitfalls:
Learners may confuse incredible with awesome because both are sometimes used informally to praise something. However, exam questions often expect the literal or core meaning of words. Another pitfall is ignoring the negative prefix in and assuming the word still carries a positive sense of belief. Paying attention to prefixes like in, un, and dis and understanding their effect on word meanings helps avoid such mistakes.

Final Answer:
The correct one word substitution for that which cannot be believed is Incredible.