Question

Mass of one atom of oxygen is:
A. $\dfrac{16}{6.023\times {{10}^{23}}}g$
B. $\dfrac{32}{6.023\times {{10}^{23}}}g$
C. $\dfrac{1}{6.023\times {{10}^{23}}}g$
D. ${{8}_{11}}$

Answer 1

Hint: In order to calculate the mass of one atom and one molecule of oxygen in kg first we will use the atomic mass of oxygen given in the periodic table and we will use the same to find the molecular mass of oxygen. As we know that atomic mass and molecular mass is given for one mole of atoms or molecules so by dividing the mass by Avagadro’s number we will find the mass of one atom and one molecule.

Complete step by step answer:
Here, we have to calculate the mass or weight of one atom of oxygen. And we know that the atomic number of oxygen is eight. It means oxygen has eight electrons and eight protons and the number of protons tells us the identity of the element, because the number of protons is the same as the atomic number.
So, the atomic mass or atomic weight of oxygen is \[8+8=16\text{ }g/mol.\] And one mol of oxygen contains a number of atoms equal to Avogadro number (N) that is $6.023\times {{10}^{23}}mo{{l}^{-1}}$
So, atomic mass of atoms of oxygen is equal to \[16g.\] As we know that atomic mass and molecular mass is given for one mole of atoms or molecules, so by dividing the mass by Avogadro’s number we will find the mass of one atom and one molecule. Mass of one atom of oxygen is:
\[=\dfrac{atomic\text{ }mass}{Avogadro\text{ }number\text{ }\left( N \right)}\]
 $\Rightarrow \dfrac{16}{6.023\times {{10}^{23}}}g$
In the calculation you should be careful that atomic mass is not equal to atomic number, it is the sum of electrons and protons. Here, we are talking about the oxygen $\left( O \right)$ element, not about the oxygen molecule ${{O}_{2}}$

So, the correct answer is Option B.

Note: Note that the sum of the masses of the elements present in the molecule. Molecular mass can be easily obtained by multiplying the given atomic mass of an element by the number of atoms contained in the molecule and then by applying the masses of all the elements in the molecule. In order to solve such types of problems students must remember the formula for molecular weight and must know the method to identify.