Which of the following is a substance that is made up of only one type of atom?

• A. Compound
• B. Element
• C. Solution
• D. Mixture

Answer: (B)

Verified step by step guidance

1. Understand the definitions of the terms: An element is a substance made up of only one type of atom, a compound consists of two or more different types of atoms chemically bonded together, and a mixture contains two or more substances physically combined but not chemically bonded.
2. Identify that the question asks for a substance made up of only one type of atom, which means it cannot be a compound or a mixture because those involve multiple types of atoms or substances.
3. Recall that an element is represented on the periodic table and consists entirely of atoms with the same atomic number, meaning only one type of atom is present.
4. Conclude that the correct choice is 'Element' because it fits the definition of a substance made up of only one type of atom.
5. Review the other options to reinforce understanding: a compound has multiple atom types bonded, and a mixture is a physical combination of substances, so neither fits the question's criteria.