Answer
a) A substance is a material where all particles share the same properties.
b) A mixture is a combination of two or more substances.
c) An element is a substance that cannot be broken down into smaller particles. Elements can be found on a periodic table.
d) A compound is a combination of two or more different elements in a fixed ratio.
Work Step by Step
a) An example of a substance is gold or water.
b) An example of a mixture is salt water or trail mix.
c) An example of an element is oxygen or argon.
d) An example of a compound is $CO_2$ or $HNO_3$.