**Introduction**
Hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3) are strong acids commonly used in chemical reactions. When these acids react with metals, they can produce hydrogen gas. However, HNO3 behaves differently compared to HCl and H2SO4 when reacting with metals. It does not produce hydrogen gas with most metals except magnesium (Mg) and manganese (Mn). This behavior can be explained by considering the nature of the acid and the specific properties of magnesium and manganese.

**1. Nature of Nitric Acid (HNO3)**
Nitric acid is a strong acid that dissociates completely in water to release hydrogen ions (H+) and nitrate ions (NO3-). The dissociation of HNO3 can be represented by the equation: HNO3 → H+ + NO3-. In aqueous solution, HNO3 exists as a hydrated hydrogen ion, known as a hydronium ion (H3O+). It is the concentration of H3O+ ions that determines the acidity of a solution.

**2. Reactivity of Metals with Acids**
When metals react with acids, they undergo a redox reaction where the metal atoms lose electrons to form positive metal ions, and hydrogen ions from the acid gain electrons to form hydrogen gas. The general equation for the reaction between a metal (M) and an acid (HX) is: M + HX → MX + H2.

**3. Lack of Reaction between Most Metals and HNO3**
Most metals do not react with HNO3 to produce hydrogen gas because nitric acid is a strong oxidizing agent. It readily oxidizes the metal atoms to their highest oxidation state, forming metal ions. The nitrate ion (NO3-) acts as a spectator ion in these reactions. The oxidation of metals by HNO3 is represented by the following equation: 3M + 4HNO3 → 3M(NO3)2 + 2H2O + N2O4.

**4. Reaction of Magnesium (Mg) with HNO3**
Magnesium is an exception to the lack of reaction with HNO3. It reacts with HNO3 to produce hydrogen gas because magnesium has a special property called passivation. Passivation is the formation of a protective oxide layer on the metal surface that prevents further reaction. In the case of magnesium, the oxide layer is not stable in the presence of nitric acid, allowing the reaction to proceed. The reaction between magnesium and HNO3 can be represented by the following equation: Mg + 4HNO3 → Mg(NO3)2 + 2H2O + N2O.

**5. Reaction of Manganese (Mn) with HNO3**
Manganese also reacts with HNO3 to produce hydrogen gas. This is because manganese has multiple oxidation states, allowing it to undergo redox reactions. In the presence of HNO3, manganese is oxidized to its highest oxidation state, which is +7. The reaction between manganese and HNO3 can be represented by the following equation: 2Mn + 8HNO3 → 2Mn(NO3)4 + 4H2O + N2O.

Because hno3 is an oxidizing agent and the hydrogen produced is oxidized and forms water