Question

Find the number of moles of sodium nitrate which contains $1.5$ moles of oxygen atoms.
A. $0.5$
B. $1.5$
C. $2.0$
D. $1.0$

Answer 1

A mole is defined as a number which is an amount of substance that contains $6.023 \times {10^{23}}$particles. It is a very convenient method to describe the number of molecules for an element or a compound. It is also very useful in concepts like POAC (principle of atomic conservation).

Complete answer:
The molecular formula of sodium nitrate is $NaN{O_3}$. It is a white solid which is readily soluble in water. It is a very good source of nitrate ion $N{O_3}^ -$, which is widely used in the reactions for the formation of fertilizers, glass, food preservatives, etc.
For the conditions given in the question, we know that
$3$moles of oxygen atom are present in $\Rightarrow 1$mole of sodium nitrate
$1$ mole of oxygen atom is present in $\Rightarrow \dfrac{1}{3}$moles of sodium nitrate
$\therefore 1.5$moles of oxygen atom will be present in $\Rightarrow \dfrac{1}{3} \times 1.5 = 0.5$moles of sodium nitrate
Hence the number of moles of sodium nitrate which contains $1.5$ moles of oxygen atoms is $0.5$moles.

So, option (a) is the correct answer.

Note:
If the number of moles of any element in the compound is asked, then initially the number of atoms present in that compound is comparable to its number of moles. For example, in water i.e., ${H_2}O$ there are 2 atoms of hydrogen and one atom of oxygen. Hence, we can say that a water molecule has 2 moles of hydrogen atom and one mole of oxygen atom respectively.