Concept:The antonym of 'boisterous' (meaning noisy and rowdy) is a word that means calm and peaceful.Explanation:Boisterous means full of noise and high energy; it is often used for a loud crowd.Placid means quiet, calm, and not easily excited. It is the direct opposite.All other options—Noisy, Clamorous, and Rowdy—are synonyms of boisterous, not antonyms.Thus, the correct choice is Placid.Answer:Option 1 (Placid)