The correct answer is 1.) A substance that gives off light
Explanation:
The word "phosphorus" is composed of the root word "phos" that derives from Greek and means light and the suffix "phoros" that means to emit or bring. This implies according to its root and composition "phosphorus" refers to something that emits light. Besides this, this word is used to describe an element or substance involved in a chemical reaction "we observed the reaction when phosphorus is exposed to oxygen"; this suggests phosphorus is a chemical compound or substance. Thus, according to its root and use in the sentence "phosphorus" is "a substance that gives off light".
