Question

Which isotope of carbon is used for getting relative atomic masses?
(A) C-12
(B) C-13
(C) C-14
(D) C-15

Answer 1

Hint: The isotope of carbon which is used to find the relative atomic masses is the most abundant isotope of carbon. Alongside this, that isotope is not a NMR active nuclei. This isotope is the most stable isotope of carbon.

Complete Step-by-Step Solution:
We will get information about the isotope which is used to find the masses of other atoms.
- We know that isotopes are the chemical species that have the same number of protons and electrons but their atomic weight is different. We are given such four isotopes of carbon.
- We know that the weights of all the atoms are decided relative to an atoms weight.
- SI decides that the isotope of carbon atom which has a molecular weight of 12 $gmmo{l^{ - 1}}$, is taken as a reference to measure the weights of other elements. SI stated that one atomic mass unit is equal to $\dfrac{1}{{12}}$ of the total mass of one atom of carbon-12. In earlier times, the oxygen-16 atom was taken as a reference to measure the weights of other elements.
- Carbon-12 has 6 protons and 6 neutrons in its structure. Its natural abundance is 98.9%. It is not radioactive.
- Carbon-13 isotope is radioactive isotope of carbon. Thus, we can conclude that the isotope of carbon which is used to find relative atomic masses is carbon-12.

So, the correct answer is (A).

Note: Note that $\dfrac{1}{{12}}$ of the mass of the single carbon-12 atom is known as atomic mass unit or amu. The value of 1 amu is $1.6605 \times {10^{ - 24}}g$. 1 amu is a unit of mass and it is equal to the value of 1 dalton.