Question

Which of the following are not in accordance with the property mentioned against them? I. \( F_2>Cl_2>Br_2>I_2 \): Oxidising power
II.\( MI>MBr>MCl>MF\): Ionic character of metal halide
III. \( F_2<Cl_2<Br_2<I_2 \): Bond dissociation enthalpy
IV. \( HI<HBr<HCl<HF \): Hydrogen-halogen bond strength

• A. I \& III only
• B. II \& III only
• C. I \& IV only
• D. II \& IV only

Hint:

Pay attention to exceptions in periodic trends like fluorine’s low bond dissociation enthalpy due to lone pair repulsion.

Answer 1

The Correct Option is B

Statement I: Oxidising power of halogens decreases down the group. \( F_2>Cl_2>Br_2>I_2 \) is correct. Statement II: The ionic character depends on the difference in size and electronegativity. MF (metal fluoride) has the highest ionic character due to the large electronegativity difference and small size of F. Hence, the given order MI>MBr>MCl>MF is incorrect. Statement III: Bond dissociation enthalpy should increase down the group. However, fluorine has anomalously low bond dissociation enthalpy due to electron-electron repulsion. The correct trend is: \( Cl_2>Br_2>F_2>I_2 \). Hence, the given order is incorrect. Statement IV: Hydrogen-halogen bond strength increases from HI to HF. So \( HI<HBr<HCl<HF \) is correct. Therefore, statements II and III are not in accordance with the given properties.