(A): Oxygen has highest tendency, among chalcogens, to form dinegative ion
(R): Electron affinity of oxygen is highest among chacogens

Options

A. Both A & R are true, R is the correct explanation of A
B. Both A & R are true, R is not correct explanation of A
C. A is true, R is false
D. A is false, R is true

Answer

To solve the question, we will analyze both the assertion (A) and the reason (R) provided in the statement.

### Step-by-Step Solution:

1. **Understanding Chalcogens**:
- Chalcogens refer to the elements in Group 16 of the periodic table, which include oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).
- Among these, oxygen is the first element.

**Hint**: Remember that chalcogens are in Group 16 of the periodic table.

2. **Assertion (A)**: "Oxygen has the highest tendency, among chalcogens, to form a dinegative ion."
- A dinegative ion is formed when an atom gains two electrons. Oxygen, having six valence electrons, tends to gain two electrons to achieve a stable octet configuration, forming the O²⁻ ion.
- Since oxygen is the smallest atom in the group, it has a higher tendency to attract electrons compared to the larger atoms below it.

**Hint**: Consider the electron configuration of oxygen and how it relates to its ability to gain electrons.

3. **Reason (R)**: "Electron affinity of oxygen is highest among chalcogens."
- Electron affinity is the energy change when an electron is added to a neutral atom. A higher electron affinity means that the atom has a stronger tendency to gain an electron.
- Oxygen has the highest electron affinity among the chalcogens because it is the smallest atom in the group, allowing it to effectively attract additional electrons.

**Hint**: Recall that electron affinity generally decreases down a group due to increasing atomic size.

4. **Conclusion**:
- Both the assertion (A) and the reason (R) are correct.
- The reason (R) correctly explains the assertion (A) because the high electron affinity of oxygen is the reason for its tendency to form a dinegative ion.

**Hint**: Look for connections between the assertion and the reason to determine if one explains the other.

### Final Answer:
Both (A) and (R) are correct, and (R) is the correct explanation of (A).