In this one word substitution question, select the single word that best replaces the phrase "That which cannot be corrected."

Introduction / Context:
This question checks your knowledge of one word substitutions for descriptive phrases. You are given the phrase "That which cannot be corrected" and asked to choose a single word that captures this idea. Such questions are common in competitive exams to see if you can link Latin based vocabulary with its simplified English definition.

Given Data / Assumptions:

• Phrase: "That which cannot be corrected."
• Options: Impregnable, Immolation, Incorrigible, Ineligible.
• We assume the phrase refers to a fault, habit, or behaviour that cannot be improved or reformed.
• The correct answer should directly express incorrigible nature.

Concept / Approach:
The adjective "incorrigible" is used for a person or habit that cannot be corrected, improved, or reformed despite repeated attempts. The prefix "in" means "not", and "corrigible" relates to being corrected. The other options have standard meanings that do not match this phrase. So you must pay attention to word roots and standard dictionary meanings rather than guessing from sound alone.

Step-by-Step Solution:
Step 1: Analyse the phrase "cannot be corrected". It implies that efforts to change or improve something fail; the nature remains the same. Step 2: Recall the meaning of "incorrigible". It describes a person or behaviour that resists all correction or reform, for example an "incorrigible liar". Step 3: Check "impregnable". This means "unable to be captured or broken into", usually used for fortresses or defences. It does not refer to correction of behaviour. Step 4: Examine "immolation". This is a noun referring to killing or offering in sacrifice, especially by burning. It is unrelated to correction. Step 5: Look at "ineligible". It means "not qualified or not allowed to do something", such as being ineligible to vote. Again, this is different from "cannot be corrected". Step 6: Therefore, "Incorrigible" is the only option that correctly matches the given phrase.

Verification / Alternative check:
Consider example sentences. A teacher might say, "He is an incorrigible mischief maker", meaning his behaviour cannot be corrected. You would not say "impregnable mischief maker" or "ineligible mischief maker" in this context. Also, newspaper articles often use "incorrigible" to describe persistent offenders. This confirms the close link between the phrase and the word in practical usage.

Why Other Options Are Wrong:
"Impregnable" belongs to the semantic field of fortifications and security, not correction or reform.

"Immolation" is about sacrifice and burning, which is conceptually far away from the idea of correction.

"Ineligible" deals with qualifications and permissions, and does not say anything about whether someone can be corrected.

Common Pitfalls:
Students can be misled by the negative prefix "in" and think that any word beginning with "in" may match the idea of "cannot". Remember that the root of the word is equally important. Recognising that "corrigible" is related to "correct" helps you see why "incorrigible" is correct here. Studying word roots and prefixes is a powerful way to improve performance on one word substitution questions.

Final Answer:
The correct one word substitute is "Incorrigible".