Question

The atomic number of carbon is $6$ and the number of neutrons is $6$. What is the atomic mass of Carbon?
A.$14\;{\text{u}}$
B.$10\;{\text{u}}$
C.$12\;{\text{u}}$
D.$11\;{\text{u}}$

Answer 1

Hint: We have to calculate the atomic mass of carbon, we should first learn what the atomic mass of an element is. The atomic mass of an element is the average mass of atoms in an element. It is measured in atomic mass units. In case of elements having isotopes, the atomic mass is calculated by taking the average of masses of isotopes multiplied by their percentage abundance in nature.

Complete answer:
In this case we are given an atomic number and a number of neutrons. We will calculate the number of protons first and then we will calculate the mass of the given element. As we know the number of protons are same as atomic number of an atom
${\text{Z}}\; = \;{\text{p}}$
${\text{p}}\; = \;6$
where ${\text{Z}}\;$is the atomic number of the element, ${\text{p}}$is the number of protons in the element. Now let’s write the given values so the number of protons in the carbon atom is $6$
atomic number of carbon, ${{\text{Z}}_{\text{C}}}\; = \;6$
number of neutrons in carbon, ${{\text{n}}_{\text{C}}}\; = \;6$
We will use the atomic mass formula to calculate the atomic mass of the carbon
${\text{M}}\; = \;{\text{n}}\; + \;{\text{p}}$
where ${\text{M}}$ is the atomic mass of an element and ${\text{n}}$is the number of protons in an element
Putting given values in the atomic mass formula we get,
${\text{M}}\; = \;6\; + \;6$
${\text{M}}\; = \;12$
so, the atomic mass of carbon is $12\;{\text{u}}$where ${\text{u}}$is the atomic mass unit.
Therefore the correct answer is option (C).

Note:
The atomic mass unit is defined as the mass which is equal to the one twelfth of mass of a carbon ${{\text{C}}^{12}}$ atom. The mass of any isotope of an element is expressed in relation to Carbon ${{\text{C}}^{12}}$ standard.