During which process is a new substance formed?

The process in which a new substance is formed is burning paper. This chemical reaction involves the paper reacting with oxygen in the presence of heat, resulting in the formation of new substances such as carbon dioxide, water vapor, ash, and various gases. Once the paper is burned, it cannot revert to its original form, illustrating a clear change at the molecular level.

In contrast, options that involve melting or boiling represent physical changes rather than chemical changes. Melting butter and melting ice involve the transition from solid to liquid states without altering the chemical structure of the substances. Similarly, boiling water leads to a change from liquid to gas but does not change the chemical composition of water; it remains H2O in all states (solid, liquid, gas). Thus, burning paper stands out as the only process among the choices that produces new substances.