Question

Define atomic mass unit.

Answer 1

An atomic mass unit is a unit of mass used to express atomic and molecular weights, equal to one twelfth of the mass of an atom of carbon-12.
OR

The atomic mass unit (amu) is defined as 1 / 12th of the mass of an atom of carbon.

$1a.m.u.=1.67\times {10}^{-24}g=1.67\times {10}^{-27}kg$