Given below are two statements: Statement I: H₂Se$\text{H}_2\text{Se}$ is more acidic than H₂Te$\text{H}_2\text{Te}$. Statement II: H₂Se$\text{H}_2\text{Se}$ has higher bond enthalpy for dissociation than H₂Te$\text{H}_2\text{Te}$. In the light of the above statements, choose the correct answer from the options given below:

Core Logic

Let us analyze the periodic properties of chalcogen hydrides (Group 16$\text{Group 16}$):

• Bond Dissociation Enthalpy (ΔdisH$\Delta_{\text{dis}}H$): As we descend the group from Selenium to Tellurium, the size of the central atom increases significantly (rTe > rSe$r_{\text{Te}} > r_{\text{Se}}$). This increase in size leads to poorer orbital overlap with the small 1s$1s$ orbital of hydrogen, resulting in a longer and weaker M-H$\text{M-H}$ bond. Consequently, the bond dissociation enthalpy decreases:

Thus, Statement II is true.

• Acidic Strength: A weaker bond dissociates more easily in aqueous solution to release H^+$\text{H}^+$ ions. Since the Te-H$\text{Te-H}$ bond is weaker than the Se-H$\text{Se-H}$ bond, H₂Te$\text{H}_2\text{Te}$ releases protons much more readily than H₂Se$\text{H}_2\text{Se}$, making it a stronger acid:

Thus, Statement I is false.

Pattern Recognition

For binary hydrides down any group (like Group 15, 16, or 17), atomic size increase weakens the covalent bond. A weaker bond releases protons more effectively, meaning that both acidic strength and reducing character increase down the group, while thermal stability decreases.

Chapter Mix

Class 12 Chemistry: p-Block Elements