b
(b)Given: Weight of iron burnt\( = 4\,g;\) Heat liberated \( = 29.28\,KJ\) and atomic weight of iron \((Fe) = 56\). We know that in ferric oxide \((F{e_2}{O_3}),\,2\,\,moles\) of iron or \(2 \times 56 = 112\,gram\) of iron are burnt. We also know that when \(4\,grams\) of iron are burnt, then heat liberated \(= 29.28\, kJ, \) therefore when \(112\,grams\) of the iron are burnt, then heat liberated \( = \frac{{29.28 \times 112}}{4} = - 819.8\,kJ\) (Minus sign due to liberation of heat).