The bond dissociation energies of `X_(2),Y_(2) and XY` are in the ratio of `1:0.5:1.` `DeltaH` for the formation of XY is -200 `kJ*mol^(-1)`. The bond dissociationn energy of `X_(2)` will be-

Options

A. `200 kJ*mol^(-1)`
B. 100 `kJ*mol^(-1)`
C. 800 `kJ*mol^(-1)`
D. 400 `kJ*mol^(-1)`

Answer

C

Explanation

`(1)/(2)X_(2)+(1)/(2)Y_(2) to XY`
`DeltaH_("reaction")=sum^((BE)_("reactant"))-sum^((BE)_("product"))` [BE=bond energy]
If bond energy of `X_(2)` is a `kJ*mol^(-1)` then bond energy of `Y_(2) and XY` are 0.5a and a `kJ*mol^(-1)` respectively.
`therefore -200=(a)/(2)+(0.5)/(2)a-a=-0.25a or, a=800`.
Therefore, bond energy of `X_(2)=800kJ*mol^(-1)`