In the following sentence, is it correct that the period is outside the quotation mark?
This powerful antioxidant flavonoid, which is actually found in a wide range of fruits and vegetables, belongs to a special class of compounds known as "Nature's Biological Response Modifiers".

Thank you for your help.
My information is that in AmE the period and comma always go inside the quotes, while in BrE they always go outside. Emotion: smile
It's a style choice: there's no "correct" and "incorrect" (except insofar as regional conventions may dictate). It's often said that putting the period (or comma) inside the quote mark is the "American" style and outside is the "British" style, but several major UK newspapers, at least, use the supposed "American" style.*

I personally put the period in the position that seems most logical, which in your example is outside the quotes: the period is not logically a part of the name of the compounds.

*Edit: Sorry, I retract that. I was trawling around to remind myself what British publications did, but the examples I looked at were actually whole quoted sentences where the period logically is a part of the quoted material (and therefore different from your example). I wasn't paying attention.
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Hi, Wordy. I researched this a bit when I first joined the site, but I can't seem to find the references which made an impression on me.

The consensus seemed to be to use your principle of logical grouping in all cases except those of the period and comma.

I confess to being weak on the rules of punctuation, and at this point mainly strive for consistency.

Best wishes, - A.Emotion: smile
AvangiThe consensus seemed to be to use your principle of logical grouping in all cases except those of the period and comma.

A BBC guide at http://www.bbc.co.uk/dna/h2g2/A41950046 extends this principle to the full stop, summarising: "...if a quote is a whole sentence, then the full stop should go inside the closing quote marks [...] However, if it's part of a sentence, it should go outside of the quote marks..."

This is my approach -- reflecting, I guess, the "British" style.
Many thanks for the reference.Emotion: happy
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I wouldn't say it's only BritEng, I was taught that way too (uppder midwest AmEng), that if the quote is only part of the sentence, the period should go outside the closing quotes.