Reactive (adjective)

1. Tending to react to a stimulus.
2. Tending to respond quickly and actively to a situation or change.

Origin:

From the latin word reactivus, from re- ("back") + agere ("to do, act").

Examples:

1. The child had a reactive temperament.
2. He had a reactive attitude to the news.
3. The substance is highly reactive.
4. The company has a reactive approach to customer complaints.
5. The market is reactive to changes in interest rates.