A : `H_(2)O` is the only hydride of chalcogen family which is liquid .
R : Acidic nature of hydrides of chalcogen family increases down the group .

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion , then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion , then mark (2)
C. If Assertion is true statement but Reason is false , then mark (3)
D. If both Assertion and Reason are false statements , then mark (4)

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that H₂O is the only hydride of the chalcogen family that is liquid.
- The chalcogen family includes oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).
- Among the hydrides of these elements, H₂O (water) is indeed the only one that exists as a liquid at room temperature.

2. **Reasoning Behind the Assertion**:
- The reason for H₂O being a liquid is due to hydrogen bonding.
- Water molecules can form hydrogen bonds with each other, which leads to a higher boiling point compared to other hydrides like H₂S (hydrogen sulfide), which is a gas at room temperature.
- Other hydrides in the chalcogen family (H₂S, H₂Se, H₂Te) do not exhibit significant hydrogen bonding, thus they remain in gaseous or solid states under normal conditions.

3. **Understanding the Reason (R)**:
- The reasoning states that the acidic nature of hydrides of the chalcogen family increases down the group.
- This means that as we move from H₂O to H₂S, H₂Se, and so on, the ability of these hydrides to donate protons (H⁺ ions) increases.

4. **Explaining the Acidic Nature**:
- When comparing H₂O and H₂S, H₂O (which forms OH⁻) is less acidic than H₂S (which forms SH⁻).
- The reason for this is that the negative charge on SH⁻ is more stable due to the larger size of sulfur compared to oxygen. This makes H₂S more willing to donate a proton than H₂O.
- This trend continues down the group with other hydrides, indicating that their acidic nature increases as we move down the group.

5. **Conclusion**:
- Both the assertion and reasoning are true statements.
- However, the reasoning provided does not correctly explain the assertion about H₂O being the only liquid hydride. The liquid state of H₂O is primarily due to hydrogen bonding, not directly related to the acidic nature of the hydrides.

### Final Answer:
- The correct evaluation is that both A and R are true, but R is not the correct explanation for A.

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