With respect to both oxygen and ozone, which one of the following statements is not correct?

Options

A. They are allotropes together
B. oxygen is colourless while ozone is coloured
C. valency of oxygen is 2 in both
D. oxygen has 2 bonds and ozone has 3 bonds

Answer

To determine which statement regarding oxygen (O2) and ozone (O3) is not correct, we will evaluate the provided statements one by one.

### Step 1: Understand Allotropes
- **Definition**: Allotropes are different forms of the same element in the same physical state.
- **Evaluation**: Oxygen (O2) and ozone (O3) are both forms of elemental oxygen. Therefore, they are allotropes.
- **Conclusion**: This statement is **true**.

### Step 2: Color of Oxygen and Ozone
- **Observation**: Oxygen (O2) is colorless, while ozone (O3) has a bluish color.
- **Evaluation**: This statement accurately describes the physical properties of both gases.
- **Conclusion**: This statement is **true**.

### Step 3: Valency of Oxygen in O2 and O3
- **Valency in O2**: In diatomic oxygen (O2), each oxygen atom has a valency of 2.
- **Valency in O3**: In ozone (O3), the central oxygen atom has a formal charge of +1 and an oxidation state of +3, which indicates that its valency is 3. The outer oxygen atoms have a valency of 2.
- **Evaluation**: The statement claiming that the valency of oxygen is 2 in both cases is incorrect.
- **Conclusion**: This statement is **false**.

### Step 4: Number of Bonds in O2 and O3
- **O2**: There is a double bond between the two oxygen atoms, which means there are 2 bonds.
- **O3**: Ozone has a resonance structure with one double bond and one single bond, resulting in a total of 3 bonds when considering resonance.
- **Evaluation**: This statement is correct.
- **Conclusion**: This statement is **true**.

### Final Conclusion
After evaluating all the statements, the statement that is not correct is the one regarding the valency of oxygen in both O2 and O3, which is option C.

### Answer
The incorrect statement is: **C. The valency of oxygen is 2 in both cases.**

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