I'm afraid it might be an adverb here, although it is in the Adjectives skill. Anyway it is utmärkt in the singular both for en and ett words, and the adverb too, but the plural or definite form is utmärkta.
en utmärkt bok 'an excellent book'
ett utmärkt svar 'an excellent answer'
två utmärkta svar 'two excellent answers'
den utmärkta boken 'the excellent book'
I am curious if "remarkable" is plausible translation. In English remarkable means "worthy of note" which can mean "excellent" as in "a remarkable tennis player" but it can also mean extraordinary as in "a remarkable scar" (you wouldn't say an excellent scar). Can utmärkt be used similarly or does it always have a connotation of being a good thing.