The bond dissociation energies of X2, Y2 and XY are in the ratio of 1 : 0.5 : 1. $\Delta$H for the formation of XY is - -200 kJ mol-1. The bond dissociation energy of X2 will he Option 1) 800 kJ mol-1 Option 2) 100 kJ mol-1 Option 3) 200 kJ mol-1 Option 4) 400 kJ mol-1

As we learnt that

Bond dissociation enthalpy -

It is the average of enthalpy required to dissociate the said bond present in different gaseous compound in to free atoms in gaseous state.

- wherein

$N_{2}+Bond\, Energy\rightarrow 2N$

$\\\frac{1}{2}X_{2} + \frac{1}{2} Y_{2}\rightarrow XY,\;\Delta H = -200\;kJ\cdot mol^{-1} \\ \Delta H = -200 = \Sigma Bond\;Energy\;Reactants -\Sigma Bond\;Energy\;Products \\* \Delta H = \frac{1}{2}\times B.E\;of\;X_{2} + \frac{1}{2}\times B.E\;of\;Y_{2} - \frac{1}{2}\times B.E\;of\;XY \\*\Delta H = \frac{1}{2}\times B.E\;of\;X_{2} + \frac{1}{2}\times B.E\;of\;X_{2}\times 0.5 - 1\times B.E\;of\;X_{2} \\* -200 = \frac{3}{4}\times B.E\;of\;X_{2} - B.E\;of\;X_{2} \\* -200 = -\frac{1}{4}\times B.E\;of\;X_{2} \\* \Rightarrow B.E\;of\;X_{2} = 800\;kJ\cdot mol^{-1}$

Option 1)

800 kJ mol-1

This is correct.

Option 2)

100 kJ mol-1

This is incorrect.

Option 3)

200 kJ mol-1

This is incorrect.

Option 4)

400 kJ mol-1

This is incorrect.

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