The value of packing fraction of carbon-12 is — Nuclear Chemistry and Radioactivity Chemistry Question

💡 Solution & Explanation

Step 1 - Packing Fraction Formula $$f = \frac{M - A}{A}$$ where $M$ = actual isotopic mass (amu), $A$ = mass number. Step 2 - Carbon-12 as Reference Standard By international convention, $1\text{ amu} \equiv \frac{1}{12}\times m(\ce{^{12}C})$. Therefore $M(\ce{^{12}C}) = 12.0000\text{ amu}$ exactly, and $A = 12$. Step 3 - Calculation $$f = \frac{12.0000 - 12}{12} = \frac{0}{12} = \boxed{0}$$ Carbon-12 has exactly zero packing fraction because it defines the atomic mass unit.