One 'u' stands for the mass of

Options

A. An atom of carbon-12
B. 1/12th of the carbon-12
C. 1/12th of hydrogen atom
D. One atom of any of the elements

Answer

### Step-by-Step Solution:

1. **Understanding 'u':**
- The symbol 'u' stands for the unified atomic mass unit, which is a standard unit of mass used to express atomic and molecular weights.

2. **Definition of Unified Atomic Mass:**
- The unified atomic mass unit (u) is defined as one twelfth (1/12) of the mass of a carbon-12 atom.

3. **Calculating 1 u:**
- To find out what 1 u represents, we can express it mathematically:
\[ 1 \, u = \frac{1}{12} \times \text{mass of a carbon-12 atom} \]
- The mass of a carbon-12 atom is taken as 12 atomic mass units (amu), hence:
\[ 1 \, u = \frac{1}{12} \times 12 \, \text{amu} = 1 \, \text{amu} \]

4. **Conclusion:**
- Therefore, 1 u is equal to the mass of one atom of carbon-12 divided by 12, which is a standard reference point for atomic mass.

### Final Answer:
One 'u' stands for the mass of \( \frac{1}{12} \) of the mass of a carbon-12 atom.