Which element is used as the standard for defining the atomic mass unit (amu)?

• A. Hydrogen
• B. Carbon
• C. Carbon-12
• D. Oxygen

Answer: (C)

Verified step by step guidance

1. Understand that the atomic mass unit (amu) is a standard unit used to express atomic and molecular weights.
2. Recall that the amu is defined based on a specific isotope of an element to provide a consistent reference.
3. Identify that the element used as the standard is Carbon, specifically the isotope Carbon-12.
4. Know that one atomic mass unit is defined as exactly \( \frac{1}{12} \) of the mass of a Carbon-12 atom.
5. Therefore, Carbon-12 serves as the reference point for all atomic mass measurements in chemistry.