Answer: a compound
Explanation:
Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Copper [tex]Cu[/tex]
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass. It can be decomposed into simpler constituents using chemical reactions. Example: Water
Ion is a specie formed when a neutral atom gains or lose electrons. [tex]Na^+[/tex]
Metal is an element which lose electrons to attain stability. Example: [tex]Na[/tex]
Atom is the smallest unit of matter which is composed of electrons, protons and neutrons.
Thus when two or more elements bond together in specific proportions, a compound is formed.
