Which of the following is an example of a chemical change?

Chemical changes occur when a substance undergoes a transformation that alters its chemical composition, resulting in the formation of one or more new substances. Rust forming on iron is a prime example of a chemical change. In this process, iron reacts with oxygen in the presence of moisture, leading to the formation of iron oxide (rust). This reaction permanently changes the properties of the original iron, indicating that a new substance has been produced.

In contrast, the other choices represent physical changes. Melting ice simply changes the state of water from solid to liquid without altering its chemical structure. Mixing sand and salt combines two substances but does not create new chemical substances; both retain their original properties and can be separated. Crushing a can modifies its physical form but does not change its chemical composition at all.