Answer: "B My youngest brother is a singer, dancer, and paints." is the sentence with the error.
Explanation: The reason why is because parallel sentences must stick with the form it started with. If all the other predicate adjectives are adjectives, then there cannot be a noun in the list of predicate adjectives. If the nouns end in -ing then all of other nouns in that list must end in -ing. All parallel sentences must stay in form with each other.