Question

The ratio of mass of nitrogen and oxygen in nitric oxide is in
(A) $ 7:16 $
(B) $ 1:8 $
(C) $ 7:8 $
(D) $ 7:15 $

Answer 1

Hint: The formula of nitric oxide is $ NO $ . We can see that the nitrogen and oxygen are present in the same ratio in the compound ( $ 1:1 $ ). The ratio of their masses will be the ratio of their respective mass fractions in the compound.

Complete step by step solution:
The given compound is nitric oxide $ NO $ . Here, the nitrogen and oxygen are present in the ratio $ 1:1 $ .
Atomic mass of nitrogen $ = 14\dfrac{g}{{gmol}} $
Atomic mass of oxygen $ = 16\dfrac{g}{{gmol}} $
Molecular mass of nitric oxide $ = 30\dfrac{g}{{gmol}} $
Mass fraction of any component in the compound $ = $ $ \dfrac{{{\text{mass of component}}}}{{{\text{mass of compound}}}} $
mass fraction of nitrogen $ = $ $ \dfrac{{{\text{atomic mass of nitrogen}}}}{{{\text{molecular mass of nitric oxide}}}} $
 $ \therefore $ mass fraction of nitrogen $ = \dfrac{{14}}{{30}} $
Mass fraction of oxygen $ = $ $ \dfrac{{{\text{atomic mass of oxygen}}}}{{{\text{molecular mass of nitric oxide}}}} $
 $ \therefore $ mass fraction of oxygen $ = \dfrac{{16}}{{30}} $
 $ \because $ ratio of mass of components $ = $ $ \dfrac{{{\text{mass fraction of first component}}}}{{{\text{mass fraction of second component}}}} $
Hence, ratio of mass fraction of nitrogen and oxygen $ = $ $ \dfrac{{{\text{mass fraction of nitrogen}}}}{{{\text{mass fraction of oxygen}}}} $
We have already calculated the mass fraction of nitrogen and oxygen. Substituting the values in the above formula:
Ratio of mass fraction of nitrogen and oxygen $ = \dfrac{{14}}{{30}} \times \dfrac{{30}}{{16}} $ $ = 7:8 $
Hence, the ratio of mass fraction of nitrogen and oxygen is $ 7:8 $ .
So, the correct option is option ©; $ 7:8 $ .

Note:
If we are asked to find the mass ratio of any two components of a compound, we can proceed by taking the atomic mass ratios. The same will be their mass ratio. The ratio has no units as they are cancelled (because they are present both in numerator and denominator).