JEE Main · 2005 · 08 May 2005 · Offline · Some Basic Concepts of Chemistry

The trap here is to imagine that changing the atomic-mass-unit standard changes the mass of a mole, but it does not. One mole of a substance is a fixed collection of molecules, an Avogadro number of them, and the combined mass of that real, counted collection is a physical quantity set by nature. Choosing to peg the unit to one-sixth rather than one-twelfth of a carbon atom only alters the numbers we write for relative atomic masses; it does not touch the actual masses of the atoms or how many of them make up a mole. So the mass of one mole of any substance stays unchanged.