What is a half-life? A. It is a rate law that is one-half order: (i. e., Rate = k[A]1/2) B. It is a special case when the rate constant equals one-half. (i. e., k = 0.5) C. A period representing the amount of time required for an initial concentration of a reactant to reduce to 0.5 M. D. A period of time required for the concentration of a reactant to reduce to one-half its original value. E. A period representing one-half the amount of time required for an initial concentration of a reactant to reduce to 0.00 M.