What contains two identical atoms?

Answer 1

Loads of stuff. Very many COMPOUNDS contain two elements.

eg Water (H and O), Methane (C and H), Carbon dioxide (C and O) etc......

Alternatively, several alloys are MIXTURES of two elements.

eg steel (iron and carbon), Bronze (copper and tin) Brass (copper and zinc) etc...

Answer 2

Anything that has two or more different types of element per particle is a compound, anything that is a mixture of two or more types of element but isn't bound together (as opposed to say, water which is bound together) is a mixture. Mixtures can also be different compounds in the same solution but not bound.

Answer 3

Diatomic molecules contain two atoms of the same element, such as H2 and O2. However, in nature the two atoms of the same element may not be identical. They may be isotopes, in which the number of neutrons differs between atoms. So a diatomic molecule consisting of two identical atoms would have to contain two atoms of the same isotope, such as two hydrogen-1 atoms or hydrogen-2 atoms. Note: The 2 after the H and O is supposed to be a subscript, representing the fact that one molecule of hydrogen contains two atoms of hydrogen, and one molecule of oxygen contains two atoms of oxygen.