Question

when oil and water are mixed, two separate layers form. each layer is called a(n) _____.
a mixture
b substance
c element
d phase

Explanation:

• A mixture is a combination of two or more substances. But the question is about each layer, not the combination of oil and water.
• A substance has a definite composition. Oil and water are substances, but the term for each layer when they are mixed (in this context) is not substance.
• An element is a pure substance made of only one type of atom. Neither oil nor water is an element.
• In physical chemistry, when two immiscible liquids (like oil and water) are mixed, they form separate layers. Each distinct layer (with uniform physical properties) is called a phase.

Answer:

d. phase