The greatest amount of energy would be obtained by the Oxidation of 100kg of

Analyze the question: We need the food that releases the most energy per unit mass when oxidized (respired or burned). Since the mass is fixed at 100 kg, this comes down to energy value per gram.

Concept: energy values of food classes

• Fats and oils (lipids): about 37-39 kJ/g (roughly 9 kcal/g)
• Carbohydrates: about 17 kJ/g (roughly 4 kcal/g)
• Proteins: about 17 kJ/g (roughly 4 kcal/g)

Fats have far more carbon-hydrogen bonds and less oxygen in their molecules than carbohydrates do. More C-H bonds are available to be oxidized, so more energy is released. Fats therefore give more than twice the energy of the same mass of carbohydrate or protein.

Step-by-step comparison of the options

• A. Meat: mainly protein, with some fat. Energy is moderate, since the protein content gives about 17 kJ/g.
• B. Butter: about 80% or more fat. It is the richest in fat, so it has the highest energy per gram.
• C. Sugar: pure carbohydrate, about 17 kJ/g. This is lower than butter.
• D. Biscuit: mostly carbohydrate with some fat, so it is mixed. Its fat content is much lower than butter's, so it gives less energy.

Answer: Butter is almost entirely fat, so 100 kg of it releases the greatest amount of energy on oxidation.

Exam tip: Whenever you see "greatest energy" in a food question, look for the option richest in fat or oil (butter, groundnut oil, palm oil, margarine). Remember: Fat = 2x energy of carbohydrate or protein.