Concept:Atomic weight (or relative atomic mass) refers to the mass of a single atom. Because macroscopic units like grams are far too large, a microscopic unit was created to express these tiny masses.
Formula:$$ \text{Unit} = \text{atomic mass unit (a.m.u)} $$
Solution:- The standard unit used to express the mass of individual atoms, molecules, or subatomic particles is the atomic mass unit (a.m.u or simply 'u').
- One a.m.u is defined as precisely \( 1/12\text{th} \) the mass of a single Carbon-12 atom.
Why other options are incorrect:- Grams / Kg: These are macroscopic units. While we have "gram-atomic mass" (the mass of an entire mole), the weight of a single atom is never practically represented in plain grams or kg without massive negative exponents.
- Mole: A unit of amount (count), not a unit of weight or mass.
Quality & Fidelity Assurance:
Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.