Which one of the following orders is not in accordance with the property stated against it ?
- F2 > Cl2 > Br2 > I2 : Bond dissociation energy
- F2 > Cl2 > Br2 > I2 : Oxidising power
- HI > HBr > HCl > HF : Acidic property in water
- F2 > Cl2 > Br2 > I2 : Electronegativity
Answer
(1) F2 > Cl2 > Br2 > I2 : Bond dissociation energy
Solution
As per NCERT, the bond dissociation enthalpy of the halogens follows the order Cl2 > Br2 > F2 > I2.
∵ In F2 the small size of fluorine causes strong repulsion between the lone pairs of the two F atoms, so the F–F bond is weaker than the Cl–Cl and Br–Br bonds.
⇒ Order (1) is not correct.
Oxidising power: F2 > Cl2 > Br2 > I2 (correct).
Acidic strength in water: HI > HBr > HCl > HF, as H–X bond strength decreases down the group (correct).
Electronegativity: F > Cl > Br > I (correct).
Answer: (1)