Assertion (A): The reducing nature of hydrides of group 16 varies in the order:
`H_2O lt H_2S lt H_2Se lt H_2Te `
Reason (R): The bond dissociation enthalpy of hydrides of group 16 decreases in the order: `H_2O gt H_2S gt H_2Se gt H_2Te. `

Options

A. Both A and Rare true and R is the correct explanation of A
B. Both A and Rare true but Ris not the correct explanation of A
C. A is true but R is false
D. A is false but R is true

Explanation

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided.

### Step 1: Understanding the Assertion (A)
The assertion states that the reducing nature of hydrides of group 16 varies in the order:
\[ H_2O < H_2S < H_2Se < H_2Te \]

**Explanation:**
- Reducing agents are substances that can donate electrons or reduce other substances while being oxidized themselves.
- In group 16, as we move down the group from oxygen to tellurium, the ability of the hydrides to act as reducing agents increases. This is because the bond strength of the H-X bond (where X is the group 16 element) decreases down the group, making it easier for the hydrogen to be released.

### Step 2: Understanding the Reason (R)
The reason states that the bond dissociation enthalpy of hydrides of group 16 decreases in the order:
\[ H_2O > H_2S > H_2Se > H_2Te \]

**Explanation:**
- Bond dissociation enthalpy is the energy required to break a bond. A higher bond dissociation enthalpy means the bond is stronger and harder to break.
- As we move down group 16, the size of the atoms increases, leading to longer and weaker bonds between hydrogen and the group 16 element. Thus, the bond dissociation enthalpy decreases.

### Step 3: Connecting Assertion and Reason
- The assertion is correct because the reducing nature increases down the group.
- The reason is also correct because it accurately describes the trend in bond dissociation enthalpy.
- Since the reason explains why the assertion is true, we conclude that both the assertion and reason are correct, and the reason is a correct explanation of the assertion.

### Conclusion
Both the assertion and reason are correct, and the reason provided correctly explains the assertion.

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

---