Question

Which of the following does not give oxygen on heating?

1. ${(N{H_4})_2}C{r_2}{O_7}$
2. $KCl{O_3}$
3. $NaN{O_3}$
4. ${K_2}C{r_2}{O_7}$

Answer 1

Oxygen rich compounds like chlorate, perchlorate ${K_2}C{r_2}{O_7}$, $KCl{O_3}$, $2NaN{O_3}$ etc. when heated undergoes decomposition and give oxygen gas $({O_2})$ but ammonium dichromate gives nitrogen gas $({N_2})$ when heated.

Complete step by step answer:
Ammonium dichromate on heating undergoes decomposition and gives Chromium (III) oxide
$(C{r_2}{O_3})$ water $({H_2}O)$ and Nitrogen gas $({N_2})$.
${(N{H_4})_2}C{r_2}{O_7} \to C{r_2}{O_7} + 4{H_2}O + {N_2} \uparrow$
When Potassium Chlorate $(KCl{O_3})$ is heated in the presence of a manganese dioxide catalyst, it breaks down to form potassium chloride (KCl) and oxygen gas $({O_2})$.
$2KCl{O_3} \to 2KCl + {O_2} \uparrow$
Sodium Nitrate compound or $NaN{O_3}$ on heating, it undergoes the decomposition reaction and then convert into compound sodium nitrite $(NaN{O_2})$ and liberating colourless and odourless oxygen gas $({O_2})$.
$2NaN{O_3} \to 2NaN{O_2} + {O_2} \uparrow$
On heating potassium dichromate $({K_2}C{r_2}{O_7})$, it decomposes to form potassium chromate, chromic oxide and oxygen gas $({O_2})$.
$4{K_2}C{r_2}{O_7} \to 4{K_2}C{r_2}{O_4} + 2C{r_2}{O_3} + 3{O_2} \uparrow$
Hence, all the given compounds are oxygen-rich. All of them, except for ammonium dichromate ${(N{H_4})_2}C{r_2}{O_7}$, gives oxygen on heating. Ammonium dichromate, on the other hand, gives nitrogen gas $({N_2})$ on heating.

Therefore, the correct answer is option (1)

Note: The thermal decomposition of ammonium dichromate ${K_2}C{r_2}{O_7}$ gives nitrogen gas $({N_2})$, and chromium (III) oxide and water and this reaction take place at a temperature of $168 - {185^\circ }C$ Pure nitrogen gas can also be obtained by heating barium aside $Ba{({N_3})_2}$ and apart from these, nitrogen gas can be obtained by the oxidation of ammonia by bromine water and by the oxidation of ammonia by hot cupric oxide, etc.