1 atomic mass unit is equal to

$\frac{1}{25}$ (mass of $F_2$ molecules) $\frac{1}{14}$ (mass of $N_2$ molecules) $\frac{1}{12}$ (mass of one $C$-atom) $\frac{1}{16}$ (mass of $O_2$ molecules)

$\frac{1}{12}$ (mass of one $C$-atom)

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