Reactive

[rɪ'æktɪv]

(adj.) participating readily in reactions; 'sodium is a reactive metal'; 'free radicals are very reactive' .

(adj.) reacting to a stimulus; 'the skin of old persons is less reactive than that of younger persons' .

Inputed by Estella--From WordNet

(a.) Having power to react; tending to reaction; of the nature of reaction.

Inputed by Franklin