Question 21

A substance with iron and nickel molecules combined but not bonded to each other

A mixture is defined as a combination of two or more substances that retain their individual properties and are not chemically bonded. In this case, iron and nickel molecules are combined without forming new chemical bonds, which exemplifies a mixture.

A) A substance with sodium and oxygen atoms bonded to each other

This option describes a compound, specifically sodium oxide, where sodium and oxygen atoms are chemically bonded. Since a compound has a fixed composition and specific properties, it does not meet the criteria for a mixture.

B) A substance with carbon and hydrogen atoms bonded together

This option represents a compound, such as hydrocarbons, where carbon and hydrogen atoms are chemically bonded. Like the previous example, this illustrates a single chemical entity rather than a mixture of different substances.

C) A substance containing only copper atoms

This option describes a pure element, specifically copper, which consists solely of one type of atom. Since it does not involve a combination of different substances, it cannot be classified as a mixture.

D) A substance with iron and nickel molecules combined but not bonded to each other

This option accurately describes a mixture, as it includes iron and nickel that are combined without forming any chemical bonds. Each element retains its individual properties, which is characteristic of a mixture.

Conclusion

The correct answer, representing a mixture, is the combination of iron and nickel that are not chemically bonded to each other. All other options describe pure substances or compounds, which do not fit the definition of a mixture since they involve chemical bonding or consist of a single type of atom. Thus, only option D fulfills the criteria for a mixture.