"One example I can think of is the expiration labels on food."
It seems like you should say "is" because "example" is a singular noun, but the sentence sounds weird to me for some reason. Maybe "the" should be removed?
"One example I can think of is the expiration labels on food."
It seems like you should say "is" because "example" is a singular noun, but the sentence sounds weird to me for some reason. Maybe "the" should be removed?
You are correct, and for the correct reason. The subject of the sentence is "example", while our object is "expiration labels". The verb should agree with the subject, not the object. A much clearer example is:
"He sees many cats."
"See" must agree with "he" not "cats". This simple intuition is just more difficult to apply when using "be" because we want the two sides to be equal.
As for your last sub-question, "the" is grammatical, but not needed. "The" can be used for both singular and plural cases. For example:
I see children outside.
I see the children outside.
Both are correct, but with slightly different meaning. The first is children in general (I probably don't know these children), while the second is a specific group of children (a group that we understand from context).
In the case of your example, we could be talking generically about "all warning labels on food", in which case we don't need "the"; or we could be talking about "the warning labels that you find on food (not on other products)", in which case we need "the".
Although it's correct to use is (because example is singular and you would never say one example are), what may be making it sound odd to you is the use of expiration labels (plural).
However, expiration dates aren't always the only thing on a food label. In fact, such dates are sometimes not even printed on labels at all but in ink straight onto the packaging.
It's also possible that you could discuss a singular referent.
Therefore, there are a few ways around this if you want to slightly rephrase the sentence it's still correct but doesn't sound a little strange:
One example I can think of is an expiration label on food.
One example I can think of is the expiration date on food labels.
One example I can think of is the expiration date on food packaging.
Without knowing the context of the text into which the sentence will fit, it's possible that any or all of these versions would be acceptable.