The average energy required to break a P-P bond in `P_(4)(s)` into gaseous atoms is `53.2 kcal mol^(-1)`. The bond dissociation energy of `H_(2)(g)` is `104.2kcal mol^(-1) , Delta H_(f)^(0)` of `PH_(3)(g)` from `P_(4)(s)` is `5.5 kcal mol^(-1)`. The P-H bond energy in kcal `mol^(-1)` is [ Neglect presence of Van der Waals force in `P_(4)(s)`]

Explanation

`nCH_(2)=CH_(2)rarr(-CH_(2)-CH_(2)-)_(n) DeltaH= -100 KJ//"mole"`
Double bond of ethylene converted to two single bonds.
`DeltaH= -100=B.E._(C-C)-2B.E._(C-C)`
`rArr -100=600-2xxB.E._(C-C)rArr B.E._(C-C)rArrB.E._(C-C)=350 kJ//"mole"`