Final answer:
Gary Soto characterizes Alfonso at the beginning of "Broken Chain" to show that Alfonso is very concerned with his physical appearance and the way others perceive him.
Step-by-step explanation:
Author Gary Soto likely opens the story "Broken Chain" with the characterization of Alfonso to establish the idea that Alfonso cares a lot about how other people see him. Alfonso's efforts to change his appearance, like pushing his crooked teeth and doing sit-ups to enhance his physique, suggest that he is deeply concerned with his physical image and the impression it makes on others, particularly girls and his peers. His desire to emulate the appearance of an Aztec warrior further underscores his concern with image and the pressure he feels to conform to certain ideals of attractiveness and toughness.