Which material is known to have the lowest density?

The material known to have the lowest density among the choices is wood. Wood is a natural material composed of cellulose fibers, which provide a lightweight structure. It typically has a density ranging from about 0.3 to 0.9 grams per cubic centimeter, depending on the type of wood.

In contrast, aluminum, although relatively lightweight compared to metals, has a density of about 2.7 grams per cubic centimeter. Steel and iron are denser materials, with steel having a density of approximately 7.8 grams per cubic centimeter and iron even higher at about 7.87 grams per cubic centimeter.

Given this context, wood's lower density makes it an excellent choice for applications where weight is a critical factor, such as in constructing lightweight structures or products. Therefore, in the context of low density materials, wood is the correct answer.