Relative susceptibility to chemical reaction(noun)
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Use "reactivity" in a sentence
"Allergic skin reactivity and chemical properties of allergens in two grades of lactose."
"Taoism especially cautions against short-term reactivity that makes you feel like you are "doing something.""
"This high reactivity is of direct importance for the catalytic activity of the enzyme, but Moore and Stein also found it possible to utilize it to label two amino acids in the active site by chemical modification."