Which of the following foods has the highest calorific value per gram?

Choosing butter as the food with the highest calorific value per gram is correct since butter is primarily composed of fats, which provide a high concentration of energy. Fats contain approximately 9 calories per gram, making them the most calorie-dense macronutrient.

In contrast, other options do not match this calorific density. Nuts, while also high in fat and caloric value, contain a mixture of protein, carbohydrates, and fiber, leading to a slightly lower calorific value per gram compared to butter. Fish and chicken, being primarily sources of protein, provide about 4 calories per gram, which is significantly lower than that of fats. Thus, the high fat content in butter contributes to its status as the highest calorific food in this context.