**Why is Hydrogen Gas Not Produced when Metal Reacts with Nitric Acid?**

When a metal reacts with an acid, hydrogen gas is usually produced as a byproduct. However, in the case of nitric acid, the reaction with metals typically does not result in the release of hydrogen gas. This is due to the unique properties and behavior of nitric acid.

**Properties of Nitric Acid:**

1. **Strong Oxidizing Agent:** Nitric acid (HNO3) is a highly reactive and powerful oxidizing agent. It readily donates oxygen (oxidation) and accepts electrons (reduction) during chemical reactions.

2. **Self-Oxidation:** Nitric acid can undergo self-oxidation, where it acts both as an oxidizing agent and a reducing agent simultaneously. This property is due to the presence of both nitrate (NO3-) and nitric oxide (NO) ions in the acid.

**Reaction with Metals:**

When a metal reacts with nitric acid, the initial reaction involves the metal displacing hydrogen from the acid to form a metal nitrate and hydrogen gas. However, in the presence of nitric acid, the hydrogen gas produced is immediately oxidized by the acid itself. This prevents the accumulation and release of hydrogen gas.

The reaction can be represented by the following equation:

Metal (M) + Nitric Acid (HNO3) → Metal Nitrate (M(NO3)2) + Nitric Oxide (NO) + Water (H2O)

In this reaction, the metal displaces hydrogen from the nitric acid to form a metal nitrate and nitric oxide gas. The nitric oxide gas produced is a reddish-brown gas and may evolve as a visible product of the reaction.

**Oxidation of Hydrogen Gas:**

The hydrogen gas produced during the reaction is oxidized by the nitric acid itself. Nitric acid acts as an oxidizing agent and readily accepts electrons from hydrogen gas, resulting in the formation of water and nitrogen dioxide gas.

2NO + 4H2O → 4HNO3 + NO2

The water formed in this reaction stays dissolved in the solution, and the nitrogen dioxide gas may evolve as a reddish-brown gas.

**Conclusion:**

In conclusion, hydrogen gas is not produced when a metal reacts with nitric acid due to the strong oxidative properties of nitric acid. The hydrogen gas formed during the reaction is immediately oxidized by the nitric acid itself, preventing its accumulation and release. This unique behavior of nitric acid distinguishes it from other acids that typically produce hydrogen gas when reacting with metals.

Nitric acid (HNO3) is a strong oxidising agent. The hydrogen gas produced during its reaction with metals gets oxidised H2O, hence no hydrogen gas is produced. Instead it involves nitric oxide such as NO2,NO etc......For eg. Cu(s)+4 HNO3(aq) ------> Cu(NO3)2 (aq)+ 2NO2 (g)+2H2O(l)