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Which one of the following orders is not in accordance with the property stated against it ?
A
$F_2 \gt Cl_2 \gt Br_2 \gt I_2$ ; Oxidising power
B
$HI \gt HBr \gt HCl \gt HF$ ; Acidic property in water
C
$F_2 \gt Cl_2 \gt Br_2 \gt I_2$ ; Electronegativity
D
$F_2 \gt Cl_2 \gt Br_2 \gt I_2$ ; Bond dissociation energy
Detailed Solution
Bond dissociation energy of the halogens: $Cl_2$ (242.6) > $Br_2$ (192.8) > $F_2$ (158.8) > $I_2$ (151.1) kJ mol$^{-1}$.
The F-F bond is unexpectedly weak because the fluorine atom is very small, so the lone pairs on the two fluorine atoms repel each other strongly.
So the order $F_2 \gt Cl_2 \gt Br_2 \gt I_2$ is not correct for bond dissociation energy.
Oxidising power decreases down the group: $F_2 \gt Cl_2 \gt Br_2 \gt I_2$; correct.
Electronegativity decreases down the group: F > Cl > Br > I; correct.
Acidic strength of the hydrogen halides in water increases as the H-X bond becomes weaker: $HI \gt HBr \gt HCl \gt HF$; correct.
So the order not in accordance with its property is the one for bond dissociation energy.
The F-F bond is unexpectedly weak because the fluorine atom is very small, so the lone pairs on the two fluorine atoms repel each other strongly.
So the order $F_2 \gt Cl_2 \gt Br_2 \gt I_2$ is not correct for bond dissociation energy.
Oxidising power decreases down the group: $F_2 \gt Cl_2 \gt Br_2 \gt I_2$; correct.
Electronegativity decreases down the group: F > Cl > Br > I; correct.
Acidic strength of the hydrogen halides in water increases as the H-X bond becomes weaker: $HI \gt HBr \gt HCl \gt HF$; correct.
So the order not in accordance with its property is the one for bond dissociation energy.