Answer the following question given this paragraph: 

Reactivity is the ability of matter to combine chemically with other substances. Some kinds of matter are extremely reactive; others are extremely unreactive. For example, potassium is very reactive, even with water. When a pea-sized piece of potassium is added to a small amount of water, it reacts explosively. You can observe this reaction in the video at the URL below. ( Caution: Don’t try this at home!) In contrast, noble gases such as helium almost never react with any other substances.


Q: The ability of matter to combine chemically with other substances is known as?


A:
reactivity