Assertion : Dinegative anion of oxygen `(O^(2-))` is quite common but dinegative anion of sulphur `(S^(2-))` is less common.
Reason : Covalency of oxygen is two.

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion
B. If both assertion and reason are true but reason is not a correct explanation of the assertion
C. If assertion is true but reason is false
D. If the assertion and reason both are false

Answer

To analyze the assertion and reason provided in the question, we will break down the statements step by step.

### Step 1: Understanding the Assertion
The assertion states that the dinegative anion of oxygen (O²⁻) is quite common, while the dinegative anion of sulfur (S²⁻) is less common.

- **Oxygen (O)** can readily gain two electrons to form O²⁻ due to its high electronegativity and small atomic size, which allows it to stabilize the negative charge effectively.
- **Sulfur (S)**, on the other hand, while it can also gain two electrons to form S²⁻, is less likely to do so because it is larger and has a lower electronegativity compared to oxygen. As a result, sulfur tends to form compounds in which it has a positive oxidation state or a lower negative oxidation state (like -2 in H₂S).

### Step 2: Understanding the Reason
The reason given is that the covalency of oxygen is two.

- Covalency refers to the number of bonds an atom can form. Oxygen typically forms two covalent bonds (for example, in water, H₂O).
- However, the reason provided does not directly explain why the dinegative anion of sulfur is less common compared to that of oxygen. While it is true that oxygen has a covalency of two, sulfur can also exhibit a covalency of two in some compounds.

### Step 3: Evaluating the Truth of Each Statement
- **Assertion**: True. The dinegative anion of oxygen (O²⁻) is common, while that of sulfur (S²⁻) is less common.
- **Reason**: True, but it does not adequately explain the assertion. The covalency of oxygen being two is correct, but it does not clarify why sulfur's dinegative state is less common.

### Conclusion
Based on the analysis:
- The assertion is true.
- The reason is true but does not provide a correct explanation for the assertion.

### Final Answer
Both the assertion and reason are true, but the reason is not a correct explanation of the assertion. Therefore, the correct option is that both statements are true, but the reason is not a correct explanation of the assertion.

---