Which of the following is an example of a solvent?

Water is the correct choice as it is a classic example of a solvent. A solvent is a substance that dissolves a solute, resulting in a solution. Water is known as the "universal solvent" because it can dissolve more substances than any other liquid, making it essential in countless chemical processes and natural phenomena. Its molecular structure allows it to interact with various solutes, such as salts and sugars, facilitating their dispersion and reactivity.

In contrast, the other substances mentioned do not fit the definition of a solvent in this context. Salt and sugar are solutes that dissolve in water, while sand is a solid that does not dissolve in liquids at typical conditions. Thus, water's unique property of dissolving many substances makes it the prime example of a solvent.