Which of these is a mixture carbon, carbon dioxide, air, and oxygen

Air is a mixture

Explanation:

Mixture is a substance which has two or more components which do not combine chemically and do not have any fixed ratio in which they are present. Example: Air

Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Carbon , Oxygen

Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: water

Thus Air is a mixture as it is composed of various gases which are not chemically bonded.

ca has a crystalline lattice with positive ions (since it is a metal, metals are positively charged) and electrons flow freely in its structure since the ca atoms have a large nuclear radius so the electrons are not tightly held, therefore the electrons can flow freely since they are not being highly attracted by the nucleus. moreover, one of the properties of metals are that they are conductors of electricity, thus proving ca is the element.