If the amount of radioactive sodium-24, used for studies of electrolytes within the body, in a sample decreases from 1.6 to 0.4 mg in 30.0 h, what is the half-life of sodium-24?

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).