Which of the following statements is/are correct?

Options

A. `NO_(2)` is a paramagnetic substance
B. NO2 solid is brown in colour
C. `NO_(2)` dimerizes to `N_(2)O_(4)`
D. `NO_(2)` is a mixed anhydride

Answer

To determine which statements regarding NO2 are correct, we will analyze each statement step by step.

### Step 1: Analyze the first statement - "NO2 is a paramagnetic substance."
- **Explanation**: To assess this, we need to look at the electron configuration of NO2. Nitrogen has five valence electrons, and in NO2, it forms one double bond with one oxygen atom and a coordinate bond with another oxygen atom. This results in one unpaired electron remaining on the nitrogen atom. The presence of unpaired electrons indicates that NO2 is paramagnetic.
- **Conclusion**: This statement is **correct**.

### Step 2: Analyze the second statement - "NO2 solid is brown in color."
- **Explanation**: NO2 is known to be a reddish-brown gas at room temperature. When it dimerizes, it forms N2O4, which is a colorless solid. Therefore, the statement that NO2 solid is brown in color is not accurate.
- **Conclusion**: This statement is **incorrect**.

### Step 3: Analyze the third statement - "NO2 dimerizes to N2O4."
- **Explanation**: At lower temperatures, two molecules of NO2 can react to form a dimer, N2O4. This reaction can be represented as:
\[ 2 NO2 \rightleftharpoons N2O4 \]
This process is well-established in chemistry.
- **Conclusion**: This statement is **correct**.

### Step 4: Analyze the fourth statement - "NO2 is a mixed anhydride."
- **Explanation**: When NO2 is dissolved in water, it can form two acids: nitrous acid (HNO2) and nitric acid (HNO3). This behavior classifies NO2 as a mixed anhydride, as it can produce more than one type of acid.
- **Conclusion**: This statement is **correct**.

### Final Conclusion:
The correct statements are:
1. NO2 is a paramagnetic substance.
2. NO2 dimerizes to N2O4.
3. NO2 is a mixed anhydride.

Thus, the correct options are **1, 3, and 4**.

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