NEETChemistryp Block Elements (Group 15, 16, 17 & 18)
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): The thermal stability of hydrogen halides decreases in the order HF > HCl > HBr > HI . Reason (R): The acidic strength of hydrogen halides increases down the group from HF to HI . In the light of the above statements, choose the most appropriate answer from the options given below.
Options
- ABoth (A) and (R) are correct and (R) is the correct explanation of (A).
- BBoth (A) and (R) are correct but (R) is NOT the correct explanation of (A).
- C(A) is correct but (R) is not correct.
- D(A) is not correct but (R) is correct.
Correct answer
B. Both (A) and (R) are correct but (R) is NOT the correct explanation of (A).
Step-by-step solution
Assertion (A) is correct: The thermal stability of hydrogen halides depends on their bond dissociation enthalpy. As the size of the halogen atom increases down the group, the H - X bond length increases and the bond dissociation enthalpy decreases. Therefore, thermal stability decreases in the order HF > HCl > HBr > HI . Reason (R) is correct: The acidic strength of hydrides depends on the ease of losing an H ^+ ion, which in turn depends on the bond dissociation enthalpy. Since the H - X bond becomes weaker down t