Question

Which of the following does not give oxygen on heating?
A. ${\rm{KCl}}{{\rm{O}}_{\rm{3}}}$
B. ${\rm{Zn}}{\left( {{\rm{Cl}}{{\rm{O}}_{\rm{3}}}} \right)_2}$
C. ${{\rm{K}}_2}{\rm{C}}{{\rm{r}}_2}{{\rm{O}}_{\rm{7}}}$
D. ${\left( {{\rm{N}}{{\rm{H}}_4}} \right)_2}{\rm{C}}{{\rm{r}}_2}{{\rm{O}}_{\rm{7}}}$

Answer 1

We can prepare oxygen by different methods including heating those compounds that have oxygen in them and can release the same upon heating.

Complete step by step solution
In synthetic chemistry we employ various methods and try to increase the effectiveness and efficiency of the same so as to get maximum yield. Our methods might vary as per our scale of production as well for example it will depend whether we are preparing our substance in lab or on industrial scale. Here, we will talk about preparation of oxygen. We know that it can be found in the combined form as oxides of metal and we can reduce these very oxides to give oxygen. For example:
${\rm{2A}}{{\rm{g}}_{\rm{2}}}{\rm{O}} \to 4{\rm{Ag}} + {{\rm{O}}_{\rm{2}}}$

In lab, we can prepare it by heating oxygen-containing compounds such as chlorates. Let’s have a look at the decomposition of given chlorates for which chemical equations are:
${\rm{2KCl}}{{\rm{O}}_{\rm{3}}} \to {\rm{2KCl}} + {\rm{3}}{{\rm{O}}_{\rm{2}}}\\\ {\rm{Zn}}{\left( {{\rm{Cl}}{{\rm{O}}_{\rm{3}}}} \right)_2} \to {\rm{ZnC}}{{\rm{l}}_{\rm{2}}} + 3{{\rm{O}}_{\rm{2}}}$

Now, let’s consider decomposition of the given chromates and we can write the chemical equations as follows:
${\rm{4}}{{\rm{K}}_2}{\rm{C}}{{\rm{r}}_2}{{\rm{O}}_{\rm{7}}} \to {\rm{4}}{{\rm{K}}_{\rm{2}}}{\rm{Cr}}{{\rm{O}}_{\rm{4}}} + {\rm{2C}}{{\rm{r}}_{\rm{2}}}{{\rm{O}}_3} + {\rm{3}}{{\rm{O}}_{\rm{2}}}\\\ {\left( {{\rm{N}}{{\rm{H}}_4}} \right)_2}{\rm{C}}{{\rm{r}}_2}{{\rm{O}}_{\rm{7}}} \to {{\rm{N}}_{\rm{2}}} + 4{{\rm{H}}_2}{\rm{O}} + {\rm{C}}{{\rm{r}}_{\rm{2}}}{{\rm{O}}_3}$

As it is evident that only potassium chromate can give oxygen not ammonium chromate as it gives nitrogen gas.
**Hence, the correct option is D.

Note:**
All the given compounds are oxygen-containing but here we have possibilities for oxidation of either nitrogen or oxygen from their combined forms to stable ones with zero oxidation state and as we can see that of nitrogen is preferred here.