Question

One atomic mass unit is _______ of the mass of one atom of _________ isotope.

• A. $2$ , hydrogen
• B. ${\frac{1}{14}}^{th}$ , carbon-14
• C. ${\frac{1}{12}}^{th}$ , carbon-12
• D. ${\frac{1}{32}}^{nd}$ , sulphur

Answer 1

The correct option is C

${\frac{1}{12}}^{th}$ , carbon-12

One atomic mass unit is ${\frac{1}{12}}^{th}$ of the mass of one atom of carbon-12 isotpoe. This implies that to get 1 unit of this mass we will have to take one carbon-12 atom, cut it up into 12 equal parts and weigh one of these parts.

For atomic mass we consider only the C-12 isotope and not C-13 or C-14 isotopes for some scientific reasons.