Explanation
Correct answer: D.
Choice D is the best answer. The convention being tested is the use of punctuation around noun phrases. No punctuation is needed because the noun phrase “aluminum oxide” is a restrictive appositive, meaning that it provides essential identifying information about the noun phrase before it, “the chemical compound,” and thus doesn’t require punctuation around it.
Why the other choices are wrong
Choice A
Choice A is incorrect because no punctuation is needed.
Choice B
Choice B is incorrect because no punctuation is needed.
Choice C
Choice C is incorrect because the noun phrase “aluminum oxide” is a restrictive appositive. Setting the phrase off with punctuation suggests that it could be removed without affecting the coherence of the sentence, which isn’t the case.