ΔH_f C₂H₄ = 12.5 kcal
Heat of atomisation of C = 171 kcal Bond energy of H₂ = 104.3 kcal Bond energy C – H = 99.3 kcal what is C = C bond energy?
(1) 140.9 kcal              (2) 49 kcal              (3) 40 kcal                  (4) 76 kcal

check your question..it must be atomisation of H₂ bond(=52.1 kcal)
see..you knw that..,

  (delta)_fH=(heat of atomisation of C)*2+(heat of atomisation of H)*4-(bond energy of C-H)*4-(bond energy of C=C)
  as C has 2 moles
H has 4 moles 
and C₂H₄ has 4 C-H bonds..
thus if u replace the values..and calculate..you are getting the value as..
(bond energy of C=C)=140.9 kcal
answer is thus (1)..
check your question..still..hope my answer helps you..^_^