Answer:
B, opposition
Step-by-step explanation:
A synonym for defiance is opposition, and we can know this because defiance means being disobedient or resistant, and opposition also means resistance towards something, which shows us that they are synonyms.
You could also get the answer through process of elimination. First, we know it can't be harmony since harmony means peace and togetherness, which is far from defiance. Peace can also be eliminated. Serenity means calm, which also wouldn't make sense. This leaves us with B, opposition.