Express unified atomic mass $\rm {unit}$ in $\rm {kg}$.

One atomic mass unit is the $\frac{1}{12}$ of the mass of a ${ }_{6} \mathrm{C}^{12}$ atom.

Mass of one mole of ${ }_{6} \mathrm{C}^{12}$ atom $=12 \mathrm{~g}$

Number of atoms in one mole

$=\text { Avogadro's number }$

$=6.023 \times 10^{23}$

$\therefore$ Mass of one ${ }_{6} \mathrm{C}^{12}$ atom $=\frac{12}{6.023 \times 10^{23}} \mathrm{~g}$

$1 \mathrm{amu}=\frac{1}{12} \times$ mass of one ${ }_{6} \mathrm{C}^{12}$ atom

$1 \mathrm{amu} =\left(\frac{1}{12} \times \frac{12}{6.023 \times 10^{23}}\right)$

$=1.67 \times 10^{-24} \mathrm{~kg}$

$=1.67 \times 10^{-27} \mathrm{~kg}$