Which of the following is an example of a reversible reaction?

An example of a reversible reaction among the given options is melting ice. This process can be reversed; when ice is heated, it melts into water, and when cooled, this water can freeze back into ice. This physical change is a classic demonstration of a reversible reaction, as it can occur in both directions without altering the chemical identity of the substance.

In contrast, the other options represent changes that are not reversible in the same way. Burning paper is a chemical change that produces ash and gases, and it cannot be reversed to reclaim the original paper. Mixing sand and salt creates a mixture that can be separated physically, but it does not involve a chemical change. Cooking an egg results in proteins denaturing, leading to a permanent change, and cannot be reversed to recover the raw egg state.