What elements do water, carbon dioxide, and rust have in common

                     The common element is Oxygen.

Explanation:

                    In order to find out the common elements between water, rust and carbon dioxide we will first write down the chemical formulas of these compounds.

                (i) Water  =  H₂O

                                           Each water molecule is made up of two atoms of hydrogen and one atom of oxygen.

                (ii) Carbon Dioxide  =  CO₂

                                            Carbon dioxide is made up of one atom of carbon and two atoms of oxygen.

                (iii) Rust =  Fe₂O₃

                                             Rust is formed when Fe (Iron) is oxidized. Hence, it is made up of two iron atoms and three oxygen atoms.

Conclusion:

                  Hence, Oxygen is the only common element found in all these three compounds.