Question

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R.

Assertion A: H₂Te is more acidic than H₂S.

Reason R: Bond dissociation enthalpy of H₂Te is lower than H₂S.

In light of the above statements, choose the most appropriate from the options given below:

• A. A is true but R is false.
• B. A is false but R is true.
• C. Both A and R are true but R is NOT the correct explanation of A.
• D. Both A and R are true and R is the correct explanation of A.

Answer 1

The Correct Option is D

Understanding Assertion A: The acidity of hydrogen compounds such as H₂S and H₂Te can be compared based on the stability of the conjugate base formed after deprotonation. H₂Te has a larger atomic size and weaker H–Te bonds compared to H–S, which leads to easier ionization of H₂Te and thus higher acidity.

Understanding Reason R: The bond dissociation enthalpy is a measure of the strength of the bond between hydrogen and the other element (S or Te). Since H–Te bonds are weaker than H–S bonds, H₂Te dissociates more easily, supporting the assertion that H₂Te is more acidic than H₂S.

Therefore, the correct interpretation of both statements shows that both Assertion A and Reason R are true, and R indeed provides the correct explanation for A.

Answer 2

Evaluate the given Assertion (A) and Reason (R) regarding the relative acidity of H₂Te and H₂S and the provided reason based on bond dissociation enthalpy.

Concept Used:

The acidity of binary hydrides (H₂X) in a group increases down the group. This is primarily because the H–X bond strength decreases down the group, making it easier to release a proton (H⁺). The bond dissociation enthalpy decreases due to the increasing atomic size of X, which leads to poorer orbital overlap with the 1s orbital of hydrogen.

Step-by-Step Solution:

Step 1: Analyze Assertion A: "H₂Te is more acidic than H₂S." This is correct. In Group 16, acidity increases down the group: H₂O < H₂S < H₂Se < H₂Te. A stronger acid has a weaker conjugate base. The conjugate base TeH^– is larger and more stable than SH^–, making H₂Te the stronger acid.

Step 2: Analyze Reason R: "Bond dissociation enthalpy of H₂Te is lower than H₂S." This is also correct. As we move down the group from S to Te, the atomic size increases significantly. This results in longer and weaker H–X bonds. Therefore, the energy required to break the H–Te bond is less than that required to break the H–S bond.

Step 3: Determine the relationship between A and R. The lower bond dissociation enthalpy of H₂Te directly facilitates the heterolytic cleavage of the H–Te bond to release H⁺, which is the very definition of acidity. Therefore, Reason R is the correct explanation for Assertion A.

Thus, both Assertion A and Reason R are correct, and Reason R is the correct explanation for Assertion A.