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In which of the following options order of arrangement does not agree with the variation of property indicated against it?
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Verified Answer
The correct answer is:
l $ < \mathrm{Br} < \mathrm{Cl} < \mathrm{F}$ (increasing electron gain enthalpy)
Electron gain enthalpy becomes less negative on moving down a group due to increase in atomic size. However, the electron gain enthalpy of $\mathrm{F}$ is less negative than $\mathrm{CI}$ due to electron-electron repulsion in small-sized $\mathrm{F}$ atom. Thus, the correct order is $\mathrm{F} < \mathrm{CI}>\mathrm{Br}>\mathrm{l}$.
$\mathrm{F}, \mathrm{CI}, \mathrm{Br}$ and $\mathrm{I}$ have $\Delta e_g H$ values (in $\mathrm{kJ}^{\mathrm{Jmol}} \mathrm{I}^{-1}$ )
$-328,-349,-325$ and -295 respectively. That order of arrangement does not agree with the variation of property.
Hence, the correct option is (3).
$\mathrm{F}, \mathrm{CI}, \mathrm{Br}$ and $\mathrm{I}$ have $\Delta e_g H$ values (in $\mathrm{kJ}^{\mathrm{Jmol}} \mathrm{I}^{-1}$ )
$-328,-349,-325$ and -295 respectively. That order of arrangement does not agree with the variation of property.
Hence, the correct option is (3).
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