The half-life of a certain radioactive element is 1250 years. what percent of the atom remains after 7500 years?

One or more substances changing into one or more substances is an example of a

Which class of molecules functions as chemical signals? hormones water carbohydrates proteins

Select all of the statements which are true. electrons are located in shells or orbits around the atom. electrons orbit slowly around the atom. electrons travel in one flat path around the nucleus of an atom. the valence of an atom is determined by the number of electrons in the atom's outermost shell.