Concept:The phrase "in need" is a fixed expression meaning lacking necessities, while "in needed" is grammatically incorrect.
Explanation:The error is in part (b) of the sentence.
The word "needed" is the past tense or past participle of the verb "need".
Here, after the preposition "in", we require a noun, not a verb form.
The standard phrase is "in need", which acts as a noun phrase meaning a state of lacking.
Example: "We help those in need."
Therefore, "in needed" should be replaced by "in need".
The corrected sentence reads: "This task is being undertaken for the benefit of young people in need at the instance of the Chief of the Group."
Answer:The error lies in part (b). So the correct option is B.