If the bond dissociation energies of `XY,X_(2)` and `Y_(2)(` all diatomic molecules `)` are in the ratio `1:1:0.5` and `Delta_(f)H` of `XY` is `-200 kJ mol^(-1)`. The bond dissociation energy of `X_(2)` will be `:`

Options

A. 100 kJ `mol^(-1)`
B. 800 kJ `mol^(-1)`
C. 300 kJ `mol^(-1)`
D. 400 kJ `mol^(-1)`

Answer

B

Explanation

`XY_((g)) rarr X_((g)) + Y_((g)), Delta H= +a` kJ/mole.....(i)
`X_(2(g)) rarr 2X_((g)), Delta H= +a` kJ/mole ...(ii)
`Y_(2(g)) rarr 2Y_((g)), Delta H= +0.5a` kJ/mole ....(iii)
`(1)/(2) xx (ii) + (1)/(2) xx (iii)- (i)`, gives
`(1)/(2) X_(2(g)) + (1)/(2) Y_(2(g)) rarr XY_((g)), Delta H= (+ (a)/(2) + (0.5)/(2)a- a)` kJ/mole
`rArr +(a)/(2)+ (0.5a)/(2)-a= -200`
`rArr a = 800`