In the following English grammar error detection question, identify the part of the sentence that contains an error, or choose "No error" if the sentence is correct: For man to change radically, fundamentally, there must be a mutation in a very brain cells of his mind.

Introduction / Context:
This question focuses on correct use of articles and determiners in English. The sentence discusses a radical change in a human being and refers to mutation in the brain cells. The test is whether you can spot the small but important error in the phrase "in a very brain cells of his mind". Correct article usage is a frequent topic in competitive English examinations.

Given Data / Assumptions:

• The sentence is split into three numbered parts plus one "No error" choice.
• The troubling phrase is "a very brain cells of his mind" in part 2 and part 3.
• The noun "cells" is clearly plural.
• The phrase should sound natural in standard formal English.

Concept / Approach:
Articles "a" and "an" are used before singular countable nouns. The definite article "the" can be used before both singular and plural nouns when referring to something specific. The word "very" in this structure functions as an intensifier meaning "exact" or "particular", as in "the very place", "the very moment", "the very words". The idiomatic pattern is "the very" followed by a noun, not "a very". Therefore we need "the very brain cells" instead of "a very brain cells". The plural noun "cells" cannot be used with the singular article "a".

Step-by-Step Solution:
Identify the noun phrase that looks wrong: "a very brain cells of his mind".Notice that "cells" is plural, so it cannot take the article "a".Recall the idiomatic expression "the very" to mean "the exact" in formal English.Replace "a" with "the" to create "the very brain cells of his mind".Confirm that, after this change, the sentence is grammatically correct and makes logical sense.

Verification / Alternative check:
With the correction, the sentence becomes "For man to change radically, fundamentally, there must be a mutation in the very brain cells of his mind." This version is natural and precise. Part 1 and part 3 do not contain any further grammatical errors. The main issue was the wrong article used before "very brain cells".

Why Other Options Are Wrong:
Part 1 uses the infinitive correctly with "For man to change radically, fundamentally," and the commas are acceptable. Part 3 contains "brain cells of his mind", which is acceptable once the article before it is fixed. Part 4, "No error", cannot be correct because a clear article error has already been identified. Therefore, the error must lie in part 2, where "a very" appears.

Common Pitfalls:
Students sometimes skim quickly and miss small function words like articles, focusing only on content words such as "mutation" and "brain cells". Others may know the phrase "very" as an adverb of degree and think that any article is acceptable before it. Remember that "very" used in the sense of "exact" almost always appears with "the", not "a", and that plural nouns cannot be preceded by "a". Training your eye to notice these patterns will make error detection questions easier.

Final Answer:
The error is in part 2 because "a very brain cells" should be "the very brain cells".