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

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Understand 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.

**Hint:** Consider the stability and formation of these anions in relation to their respective elements.

### Step 2: Analyze the Dinegative Anion of Oxygen
Oxygen, being highly electronegative, readily gains two electrons to form the O²⁻ anion. This high electronegativity allows oxygen to stabilize the additional negative charge effectively.

**Hint:** Reflect on the concept of electronegativity and how it influences an element's ability to gain electrons.

### Step 3: Analyze the Dinegative Anion of Sulfur
Sulfur, while it can also form a dinegative anion (S²⁻), does not do so as readily as oxygen. This is primarily due to its lower electronegativity compared to oxygen, which makes it less favorable for sulfur to gain two electrons.

**Hint:** Think about the periodic trends in electronegativity and how they apply to sulfur compared to oxygen.

### Step 4: Understand the Reason
The reason provided states that the covalency of oxygen is two. While this is true, it does not directly explain why O²⁻ is more common than S²⁻. Covalency refers to the number of bonds an atom can form, which is related but not the sole reason for the stability of the anion.

**Hint:** Consider whether covalency directly influences the formation of dinegative anions or if other factors like electronegativity play a more significant role.

### Step 5: Conclusion
Both the assertion and the reason are true statements. However, the reason does not adequately explain the assertion regarding the commonality of the dinegative anions. Therefore, the correct answer is that both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

**Final Answer:** Option B - Both assertion and reason are true, but the reason is not the correct explanation of the assertion.