Answer:
Noun.
Explanation:
A part of speech is one of the eight "parts" of the speech in grammar. The parts of speech tell us the function of the given word(s), their meaning grammatically in a sentence.
The 8 parts of speech are noun, pronoun, verb, adverb, adjective, preposition, conjunction, interjection, etc.
And in the given sentence "Mr. Jones is a helpful teacher", Mr. Jones is the subject of the sentence, and also a noun, a proper noun as it is the name of a particular person. The word "is" is a helping verb, "a" is an article, "helpful" is an adjective as it describes the objective noun "teacher".
Thus, the correct answer is a noun.
