Match these terms and definitions. 1. the smallest complete unit of a compound or diatomic gas compound 2. a new substance formed by the combination of two or more different atoms element 3. path of electrons around an atomic nucleus molecule 4. a substance consisting of only one type of atom shell

Terms matched with the right definitions;

A molecule is the smallest unbreakable unit of a specific element or compound that retains the chemical properties of that element or compound. Molecules are composed of two or more atoms that are joined together by chemical bonds. An example of a molecule is H2O (water) which contains two hydrogen atoms and one oxygen atom.

A compound is a chemical substance that is formed by the combination of many identical molecules that contains atoms from more than one element which are held together by chemical bonds that are difficult to break. An example of a compound is NaCl, which is composed of sodium and chlorine.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

"a.) well–developed vascular system."