Which of the following statements BEST describes a mixture? А
Carbon dioxide is an example of a heterogeneous mixture.
B
A compound and a mixture are the same type of substance.
Two elements that are in the area but not chemically combined can be a mixture.
D
A mixture is unable to be separated because the molecules have been chemically combined.

C) Two elements that are in the area but not chemically combined can be a mixture

Explanation:

An example of a mixture would be salt and water. The salt particles dissolve into the water but no chemical change has happened. I mean that no new chemical compound is made and also heat/energy is not given off. Furthermore, we can separate the two items (for instance through evaporation) and those two items retain their original properties. This helps show that the salt and water particles don't form a bond and we can separate those particles apart so to speak.

Another example of a mixture is iron and plastic. We can pull out the iron through using a strong magnet. Whether or not the iron is with the plastic, the iron retains its properties. The same can be said of the plastic. The two materials just happen to occupy the same space or volume or area.

If you have two chemicals react in some way to form a new chemical, then this is not a mixture. For instance if we combine vinegar and baking soda, it produces carbon dioxide and water. There isn't a process to undo this to get the vinegar and baking soda back (like there was a process to get the iron separated).