Which substance is a combination of different atoms?
a.) homogeneous mixture
b.) heterogeneous mixture
c.) element
d.) compound

The substance which is a combination of different atoms is

compound

compound is substance formed when two ore more different atoms are chemically bonded together. example of compound H20 which is made up of which is made of two atoms of hydrogen and one atom of oxygen joined by a covalent bond to form water(H20)

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.