Responsive and Reactant

adjective

• Containing or using responses; alternating.
  • usage: "responsive reading"; "antiphonal laughter"
  • synonyms: antiphonal
• Readily reacting or replying to people or events or stimuli; showing emotion.
  • usage: "children are often the quickest and most responsive members of the audience"
• Reacting to a stimulus.
  • usage: "the skin of old persons is less reactive than that of younger persons"
  • synonyms: reactive

• (a.) That responds; ready or inclined to respond.
• (a.) Responsible.
• (a.) Suited to something else; correspondent.

noun

• A chemical substance that is present at the start of a chemical reaction. .