Apure substance made up of only one type of atom is a(n)
a. mixture.
b. element.
c. compound.
d. proton or neutron.

element

Explanation:

Element is a pure substance which is composed of similar or one type of atoms.It can not be decomposed into simpler constituents using chemical reactions.Example: Gold

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: carbon dioxide

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