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NEET CHEMISTRYMedium

Which one of the following orders is not in accordance with the property stated against?

A

F2>Cl2>Br2>I2F_2 > Cl_2 > Br_2 > I_2: Oxidising power

B

HI>HBr>HCl>HFHI > HBr > HCl > HF: Acidic property in water

C

F2>Cl2>Br2>I2F_2 > Cl_2 > Br_2 > I_2: Electronegativity

D

F2>Cl2>Br2>I2F_2 > Cl_2 > Br_2 > I_2: Bond dissociation energy

Step-by-Step Solution

Let's analyze the properties of halogens (Group 17):

  1. Oxidising Power: Fluorine is the strongest oxidising agent, and oxidising power decreases down the group (F2>Cl2>Br2>I2F_2 > Cl_2 > Br_2 > I_2) as standard electrode potentials decrease (+2.87 V to +0.54 V). This order is correct .
  2. Acidic Property: The acidic strength of hydrohalic acids depends on the bond dissociation enthalpy. As the bond dissociation enthalpy decreases down the group (HF>HCl>HBr>HIH-F > H-Cl > H-Br > H-I), the bond breaks more easily, releasing H+H^+ ions. Thus, acidic strength increases: HF<HCl<HBr<HIHF < HCl < HBr < HI. This order is correct .
  3. Electronegativity: Electronegativity decreases down the group as atomic size increases. The order is F>Cl>Br>IF > Cl > Br > I. This order is correct .
  4. Bond Dissociation Energy: The bond dissociation enthalpy of F2F_2 is anomalously low (155 kJ/mol) compared to Cl2Cl_2 (243 kJ/mol) and even Br2Br_2 (192 kJ/mol). This is due to the relatively large electron-electron repulsion among the lone pairs in the small F2F_2 molecule. The correct order is Cl2>Br2>F2>I2Cl_2 > Br_2 > F_2 > I_2. Therefore, the order F2>Cl2>Br2>I2F_2 > Cl_2 > Br_2 > I_2 is incorrect .
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