The relative atomic mass of Carbon-12 is taken as:

**The reasoning** Carbon-12 is the **standard reference** for atomic mass. Scientists chose it as the benchmark against which all other atomic masses are measured. By international agreement, one atom of Carbon-12 is assigned a mass of **exactly 12 atomic mass units (amu)**. This is a definition, not a calculation. Think of it like this: just as we defined 1 meter or 1 kilogram as our measurement standards, we defined Carbon-12 = 12 amu as our atomic mass standard. Everything else (hydrogen ≈ 1, oxygen ≈ 16, etc.) is measured *relative to* this Carbon-12 standard. **Why the wrong options tempt you** - **Option A (1)**: You might confuse this with hydrogen, which has atomic mass ≈ 1, or think "relative" means starting from 1. - **Option B (6)**: This is carbon's *atomic number* (number of protons), not its atomic mass. Classic mix-up! - **Option D (14)**: This is Carbon-14, a different isotope used in radiocarbon dating. Wrong carbon! **Quick takeaway** Carbon-12 is the *definition* of atomic mass — it equals exactly 12 amu by international agreement, making it the ruler by which all other atoms are measured.