Question

air contains oxygen, nitrogen, hydrogen and water vapor. none of these are chemically combined. which of the following best describes air: pure substance compound heterogeneous mixture homogeneous mixture

Explanation:

A pure substance has a uniform and definite composition. A compound is a pure substance formed by chemical combination of elements. A heterogeneous mixture has visibly different substances or phases. A homogeneous mixture has a uniform composition throughout. Air has multiple components (oxygen, nitrogen, hydrogen, water vapor) not chemically combined and has a uniform composition (on a large - scale, we can't see distinct layers of these gases), so it is a homogeneous mixture.

Answer:

homogeneous mixture