Question

when the elements copper (cu) and oxygen (o) chemically combine, they form_
options:
a mixture
an ion
a gas
a compound

Explanation:

When two elements (copper and oxygen) chemically combine, they form a compound. A mixture is a physical combination, an ion is a charged particle, and a gas is a state of matter. Chemical combination of elements forms a compound (like copper oxide).

Answer:

a compound