The correct option is **C. Copper**. ### Explanation of the Correct Answer **1. Understanding Passivity:** Passivity refers to the phenomenon where a metal becomes resistant to corrosion or further reaction in a particular environment, often due to the formation of a protective oxide layer. In the case of concentrated trioxonitrate (V) acid (commonly known as concentrated nitric acid), certain metals can form a passive layer that prevents further reaction. **2. Behavior of Each Metal in Concentrated Nitric Acid:** - **Iron (A):** Iron reacts with concentrated nitric acid, forming iron(III) nitrate and releasing nitrogen oxides. It does not exhibit passivity in this environment. **Reaction:** \[ \text{Fe} + 4 \text{HNO}_3 \rightarrow \text{Fe(NO}_3\text{)}_3 + 2 \text{NO}_2 + 2 \text{H}_2\text{O} \] - **Tin (B):** Tin can also react with concentrated nitric acid, although it is less reactive than iron. It can form a protective oxide layer, but it is not completely passive and can still react under certain conditions. **Reaction:** \[ \text{Sn} + 4 \text{HNO}_3 \rightarrow \text{Sn(NO}_3\text{)}_2 + 2 \text{NO}_2 + 2 \text{H}_2\text{O} \] - **Copper (C):** Copper is known to be passive in concentrated nitric acid. It forms a protective layer of copper(II) oxide (CuO) or copper(II) nitrate, which prevents further reaction with the acid. This passivity is a key characteristic of copper in this environment. **Reaction:** \[ \text{Cu} + 4 \text{HNO}_3 \rightarrow \text{Cu(NO}_3\text{)}_2 + 2 \text{NO}_2 + 2 \text{H}_2\text{O} \] - **Zinc (D):** Zinc reacts vigorously with concentrated nitric acid, producing zinc nitrate and nitrogen oxides. It does not exhibit passivity in this environment. **Reaction:** \[ \text{Zn} + 4 \text{HNO}_3 \rightarrow \text{Zn(NO}_3\text{)}_2 + 2 \text{NO}_2 + 2 \text{H}_2\text{O} \] ### Why Other Options Are Incorrect or Weaker - **Option A (Iron):** Iron is not passive in concentrated nitric acid; it actively reacts and corrodes, producing nitrogen oxides. Therefore, it cannot be considered passive. - **Option B (Tin):** While tin can form a protective oxide layer, it is not completely passive and can still react under certain conditions, making it less suitable than copper. - **Option D (Zinc):** Zinc reacts readily with concentrated nitric acid, showing no signs of passivity. It is highly reactive and thus not a candidate for passivity. ### Summary of Key Points - **Passivity** is the resistance of a metal to corrosion due to a protective layer. - **Copper** is passive to concentrated nitric acid, forming a protective layer that prevents further reaction. - **Iron, Tin, and Zinc** do not exhibit passivity in concentrated nitric acid; they react and corrode. - Understanding the behavior of metals in acidic environments is crucial for predicting their reactivity and stability. ### Revision Summary - Passivity refers to a metal's resistance to corrosion due to a protective layer. - Copper is passive in concentrated nitric acid, while iron, tin, and zinc are not. - Reactions of metals with concentrated nitric acid vary, affecting their passivity. - Always consider the specific conditions and reactions when assessing metal behavior in acids.