When zinc reacts with dilute HNO3, it will produce nitrous oxide gas. At room temperature, it is a colourless, non-flammable gas, with a pleasant, slightly sweet odor.
4‌Zn+
10HNO3
Warm‌dilute
→
4‌Zn(NO3)2
Zinc‌nitrate
+NH4NO3+3H2O
4‌Zn+
10HNO3
Cold‌dilute
→
4‌Zn(NO3)2
Zinc‌nitrate
+
N2O
Nitrous‌oxide
+5H2O
Similarly, when zinc reacts with concentrated HNO3, it will produce nitrogen dioxide gas (NO2). It is used as the indicator for the larger group of nitrogen oxides.