Which of the following statements is incorrect ?

Options

A. The superoxide ion (i.e. , `O_2^-`) radius is greater than Oxygen atom radius .
B. Alkali metals are normally kept in kerosene oil
C. All the alkali metal hydrides are ionic solids with high melting points
D. The concentrated solution of alkali metals in liquid ammonia are paramagnetic in nature.

Explanation

To solve the question "Which of the following statements is incorrect?", we will analyze each statement provided and determine their validity.

### Step-by-Step Solution:

1. **Analyzing the First Statement:**
- Statement: "The superoxide ion \( O_2^{-} \) radius is greater than the oxygen atom radius."
- Explanation: In general, the radius of an anion is larger than that of its neutral parent atom because when an atom gains an electron to form an anion, the increased electron-electron repulsion and the unchanged nuclear charge result in a larger radius. Therefore, this statement is **true**.

2. **Analyzing the Second Statement:**
- Statement: "Alkali metals are normally kept in kerosene oil."
- Explanation: Alkali metals are highly reactive with air and water, which can lead to dangerous reactions. To prevent this, they are stored in inert solvents like kerosene oil. Thus, this statement is also **true**.

3. **Analyzing the Third Statement:**
- Statement: "All the alkali metal hydrides are ionic solids with high melting points."
- Explanation: Alkali metal hydrides are indeed ionic due to the larger size of alkali metals and their low ionization energy. The strong ionic bonds result in high melting points. Therefore, this statement is **true**.

4. **Analyzing the Fourth Statement:**
- Statement: "The concentrated solution of alkali metal in liquid ammonia are paramagnetic in nature."
- Explanation: In dilute solutions of alkali metals in liquid ammonia, the presence of unpaired ammoniated electrons makes them paramagnetic. However, in concentrated solutions, these unpaired electrons pair up, leading to a diamagnetic nature. Therefore, this statement is **incorrect**.

### Conclusion:
The incorrect statement is the fourth one: "The concentrated solution of alkali metal in liquid ammonia are paramagnetic in nature."

### Final Answer:
The answer is option 4.

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