An increase in the number of protons, when unaccompanied corresponding

This one was easy ,

For subject -verb agreement we need 'produces' so scanning choices only E and C are left . Then C is out because of "when that " .

Reading back E makes perfect sense in sentence

Increase needs singular verb produces thereby we can eliminate A,B and D.
Usage of when that indicates pronoun error as that cannot be used to refer to when and when cannot refer to the no of protons.
This eliminates option C.

An increase ---> produces (not produce)

This leaves us with options C and E.

"not accompanied" is more preferred over "unaccompanied"

OE:
The “when”/”if” split at the beginning tells us nothing: either one of those could be correct.

Split #1: let’s start with the meat-and-potato grammatical issue of subject-verb agreement. The subject of the sentence is “increase”, which is singular, so we need a singular verb. Choices (A) & (B) & (D) have the plural verb “produce”, which is incorrect; only (C) & (E) have the correct singular verb, “produces.”

Split #2: “correspondingly” vs. “corresponding”. This is a very tricky split. The word “correspondingly” is an adverb, and so must modify a verb or participle --- here, it would have to modify “unaccompanied.” The word “corresponding” is an adjective, and so it must modify a noun ---- here, it would have to modify the second appearance of the word “increase.” We can ask the simple question: what corresponds to what? what matches what? Well, we are talking about an increase in one thing is matched by an increase in another ---- the two increases are “corresponding.” By contrast, there is something bizarrely illogical about “unaccompanied correspondingly” ---- “unaccompanied” means two things don’t go together, and “correspondingly” means the two things do go together, so in this sense, “unaccompanied correspondingly” is an inherent contradiction. We will reject choices (A) and (C) which have this phrase.

This leaves (E) as the only possible grammatical correct answer.

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