Final answer:
Eight elements, with oxygen and silicon being the most abundant, comprise about 98% of the earth's crust by weight and volume.
Step-by-step explanation:
There are eight chemical elements that make up approximately 98% of the earth's crust. These elements, in order of abundance, are oxygen, silicon, aluminium, iron, calcium, sodium, potassium, and magnesium. Oxygen is the most abundant, constituting about 47% by weight and 94% by volume of the earth's crust. Silicon follows, making up about 28% by weight.
These elements are usually found in compound forms, with oxygen combined with other elements, particularly with silicon to form various minerals that make up rocks, soil, and clays. This is due to the fact that the earth's crust is composed almost entirely of minerals, where silicon atoms are often at the center of the silicon-oxygen tetrahedron.