Which of the following is proper grammar usage?
1 in 7 apples becomes green
1 in 7 apple becomes green
1 in 7 apples become green
One in seven apples becomes green.
("One in seven apples" means "one [apple] in seven apples"; the "apples" belongs to the "seven", but the verb agrees with the "one [apple]".)
Edited to add: Maybe there's a dialectal difference, or other point of disagreement? Edwin Ashworth links to a similar question whose answers, and their vote-counts, seem to suggest a division between those who agree with me and those would accept "One in seven apples become green." I'm still inclined to recommend becomes, because I know that some speakers accept only become and I do not know whether any accept only become, but that's a recommendation grounded in uncertainty. Hopefully someone can provide more useful evidence.
The phrase "1 in 7" is basically expressing a fraction, not a count. It is not the equivalent of "one", it is the equivalent of "1/7 of the population".
Replace "1 in 7" with "Some" and see what sounds better
Some apples become green.
Some apples becomes green.
"Some apples" is plural, so the plural form of the verb holds.
Howevever, if the phrase was "1 of the 7 apples becomes green" that would be the singular case.
1 in 7 apples becomes green.
The subject is singular, therefor use the singular version of the verb "become". Example: A cat becomes fat. Cat as the subject of this sentence is singular. Therefore the sentence requires the singular version of the verb. If you want to debate what the actual subject of the sentence in question is, know this: "... in 7 apples" is a prepositional phrase and cannot be the subject. Thus, the easy answer to "What is the subject of this sentence?" becomes (haha) "1". Use the singular version of the verb! :)
--Sorry to answer whether to use apples or apple, know this: "7" modifies apples, so apples has to be plural. "1" is the subject, and "in 7 apples" is a prepositional phrase modifying the subject.
1 in 7 apples becomes green.
Maybe the best way to answer this is to understand what the sentence really means : among seven apples, only one becomes green, while the six others don't.
As you can see, the answer is obvious, which is "1 in 7 apple*s* become*s* green" and any other form is simply wrong and/or meaningless.
One apple in seven becomes green.
The singular verb is correct. The scenario is repeating many times, but In each set of seven apples, one apple becomes green. The subject of becomes is one apple.
Or
One seventh of the apples become green.
Now you are talking about the group becoming green, and that group is a number of apples all becoming green. So the plural verb is used.