This is the 14951st most frequent Korean word.
반응이다
"반응이다" means "to respond" or "to react."
반응이었다 is used here to describe the nature of the response as a reaction, highlighting its promptness.
그의 대답은 빠른 반응이었다.
His answer was a quick reaction.
반응 is used to refer to the opinions or feelings people express in response to the event.
저 사건에 대한 사람들의 반응이 궁금하다.
I am curious about people's reactions to that event.
반응 is used in an instructional context, asking for a reaction to an issue but specifically emphasizing creativity.