$$\left(\mathrm{NH}_4\right)_2 \mathrm{Cr}_2 \mathrm{O}_7$$ on heating liberates a gas. The same gas will be obtained by
- Aheating $$\mathrm{NH}_4 \mathrm{NO}_2$$
- Btreating $$\mathrm{H}_2 \mathrm{O}_2$$ with $$\mathrm{NaNO}_2$$
- Ctreating $$\mathrm{Mg}_3 \mathrm{~N}_2$$ with $$\mathrm{H}_2 \mathrm{O}$$
- Dheating $$\mathrm{NH}_4 \mathrm{NO}_3$$
✓ Correct answer: A
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