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p-Block Elements appeared 42 times across 3 years — 4.9% of Chemistry. This question is from Group 16 Hydrides.

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Questions 16 13 13 42
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Given below are two statements: Statement I: H₂Se is more acidic than H₂Te. Statement II: H₂Se has higher bond enthalpy for dissociation than H₂Te. In the light of the above statements, choose the correct answer from the options given below:

Solution & Explanation

Core Logic

Let us analyze the periodic properties of chalcogen hydrides (Group 16):

  • Bond Dissociation Enthalpy (ΔdisH): As we descend the group from Selenium to Tellurium, the size of the central atom increases significantly (rTe > rSe). This increase in size leads to poorer orbital overlap with the small 1s orbital of hydrogen, resulting in a longer and weaker M-H bond. Consequently, the bond dissociation enthalpy decreases:
ΔdisH: H₂Se (276 kJ mol⁻¹) > H₂Te (238 kJ mol⁻¹)

Thus, Statement II is true.

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

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

Reference Study Guides

P Block Elements

More p-Block Elements Previous-Year Questions — Page 8

Q79 jee_main_2024_30_january_evening Group 15 Hydrides
Choose the correct statements about the hydrides of group 15 elements. A. The stability of the hydrides decreases in the order NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃ B. The reducing ability of the hydrides increases in the order NH₃ < PH₃ < AsH₃ < SbH₃ < BiH₃ C. Among the hydrides, NH₃ is strong reducing agent while BiH₃ is mild reducing agent. D. The basicity of the hydrides increases in the order NH₃ < PH₃ < AsH₃ < SbH₃ < BiH₃ Choose the most appropriate from the option given below:
  • A. B and C only
  • B. C and D only
  • C. A and B only
  • D. A and D only

Solution

Core Logic

Statement A: As we move down Group 15, the size of the central atom increases, causing the E-H bond length to increase and its bond strength to decrease. Thus, thermal stability decreases in the order: NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃. Statement A is correct.

Statement B: Because the E-H bond strength decreases down the group, it becomes easier to release hydrogen. Therefore, the reducing ability increases down the group: NH₃ < PH₃ < AsH₃ < SbH₃ < BiH₃. Statement B is correct.

Statement C: Following the logic from B, NH₃ is a very weak reducing agent (mild), while BiH₃ is the strongest reducing agent among them. Statement C is false.

Statement D: Basicity depends on the availability of the lone pair for donation. In NH₃, the lone pair is concentrated in a small sp³ orbital (high electron density). Moving down the group, the lone pair occupies larger orbitals with more s-character (Drago's rule), decreasing electron density and making the lone pair less available. Thus, basicity decreases down the group. Statement D is false.

Step 1: Final Conclusion

Only statements A and B are correct.

Chapter Mix

Class 12 Chemistry: The p Block Elements

Q64 jee_main_2024_30_jan_morning Group 15 Elements
Given below are the two statements: one is labeled as Assertion (A) and the other is labeled as Reason (R). Assertion (A): There is a considerable increase in covalent radius from N to P. However from As to Bi only a small increase in covalent radius is observed. Reason (R): covalent and ionic radii in a particular oxidation state increases down the group. In the light of the above statement, choose the most appropriate answer from the options given below:
  • A. (A) is false but (R) is true
  • B. Both (A) and (R) are true but (R) is not the correct explanation of (A)
  • C. (A) is true but (R) is false
  • D. Both (A) and (R) are true and (R) is the correct explanation of (A)

Solution

Core Logic

Assertion (A) is a factual statement directly from NCERT: In Group 15, there is a large increase in covalent radius from Nitrogen to Phosphorus, but from Arsenic to Bismuth, the increase is very small. Reason (R) states that covalent and ionic radii increase down the group. This is a generally true statement.

Step 1: Explaining the discrepancy

While (R) is a true general trend, it does not correctly explain the anomaly highlighted in (A). The correct explanation for the small increase in radius from As to Bi is the poor shielding effect of completely filled d and f-orbitals in the heavier members, leading to a higher effective nuclear charge (Zeff).

Final Conclusion

Therefore, both (A) and (R) are true, but (R) is not the correct explanation for (A).

Pattern Recognition

Whenever radius anomalies occur in heavier p-block elements (like small increases), the underlying cause is almost always d-block or f-block contraction (poor shielding).

Chapter Mix

Class 12 Chemistry: The p-Block Elements

Q jee_main_2024_31_jan_evening Oxygen Family (Group 16 Elements)
Choose the correct statements from the following A. All group 16 elements form oxides of general formula EO₂ and EO₃ where E = S, Se, Te and Po. Both the types of oxides are acidic in nature. B. TeO₂ is an oxidising agent while SO₂ is reducing in nature. C. The reducing property decreases from H₂S to H₂Te down the group. D. The ozone molecule contains five lone pairs of electrons. Choose the correct answer from the options given below:
  • A. 1. A and D only
  • B. 2. B and C only
  • C. 3. C and D only
  • D. 4. A and B only

Solution

Core Logic

(A) All group 16 elements form oxides of the EO₂ and EO₃ type where E = S, Se, Te or Po. These are generally acidic in nature. (Correct) (B) SO₂ is reducing while TeO₂ is an oxidising agent due to the inert pair effect increasing the stability of lower oxidation states down the group. (Correct) (C) The reducing property increases from H₂S to H₂Te down the group because the E-H bond dissociation enthalpy decreases as atomic size increases. (Incorrect) (D) The ozone molecule (O₃) has the structure O=O^+-O^-. Counting the lone pairs: the central oxygen has 1, the double-bonded oxygen has 2, and the single-bonded negatively charged oxygen has 3. Total lone pairs = 1 + 2 + 3 = 6. (Incorrect)

Step 1: Final Selection

Since A and B are the only correct statements, option 4 is the right choice.

Chapter Mix

Class 12 Chemistry: The p-Block Elements

Q jee_main_2024_31_jan_evening Group 13 Elements (Boron Family)
Given below are two statements: Statement I: Group 13 trivalent halides get easily hydrolyzed by water due to their covalent nature. Statement II: AlCl₃ upon hydrolysis in acidified aqueous solution forms octahedral [Al(H₂O)₆]³⁺ ion. In the light of the above statements, choose the correct answer from the options given below:
  • A. Statement I is true but statement II is false
  • B. Statement I is false but statement II is true.
  • C. Both statement I and statement II are false.
  • D. Both statement I and statement II are true.

Solution

Core Logic

Statement I: In the trivalent state, most compounds of Group 13 elements (like BCl₃, AlCl₃) are covalent due to small cation size and high charge, and they are readily hydrolysed in water. Thus, Statement I is true.

Statement II: Trichlorides on hydrolysis in normal water can form tetrahedral [M(OH)₄]^- species depending on pH, but in an acidified aqueous solution, aluminium forms the octahedral [Al(H₂O)₆]³⁺ ion where the hybridization state of Al is sp³d². Thus, Statement II is also true.

Step 1: Final Conclusion

Both Statement I and Statement II are correct, pointing to option (4).

Chapter Mix

Class 11 Chemistry: The p-Block Elements

Q64 jee_main_2024_31_jan_evening Properties of Sulphur and Halogens
Given below are two statements: Statement I: S₈ solid undergoes disproportionation reaction under alkaline conditions to form S²⁻ and S₂O₃²⁻ Statement II: ClO₄^- can undergo disproportionation reaction under acidic condition. In the light of the above statements, choose the most appropriate answer from the options given below:
  • A. Statement I is correct but statement II is incorrect.
  • B. Statement I is incorrect but statement II is correct
  • C. Both statement I and statement II are incorrect.
  • D. Both statement I and statement II are correct.

Solution

Core Logic

Statement I: S₈ disproportionates in alkaline medium to give sulphide (S²⁻) and thiosulphate (S₂O₃²⁻). The reaction is:

S₈ + 12OH^- arrow 4S²⁻ + 2S₂O₃²⁻ + 6H₂O

This is a correct statement.

Statement II: ClO₄^- contains chlorine in its highest possible oxidation state of +7. A species can undergo disproportionation only if the element can exist in both higher and lower oxidation states than the present one. Since chlorine cannot exceed +7, ClO₄^- cannot undergo disproportionation. This is an incorrect statement.

Step 1: Final Conclusion

Statement I is correct, and Statement II is incorrect. Therefore, option (1) is the correct answer.

Chapter Mix

Class 11 Chemistry: Redox Reactions Class 12 Chemistry: The p-Block Elements

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