Among the following foods, which one has the lowest calorific value per gram?

Milk is the food item with the lowest calorific value per gram among the options provided. It is primarily composed of water, carbohydrates (in the form of lactose), proteins, and fat, but the fat content in milk is generally lower than that found in cheese, butter, or chocolate.

Cheese and butter have significantly higher fat content, leading to a much higher caloric density. For instance, butter is almost entirely fat, and cheese, while it contains protein and some carbohydrates, still has a high fat content that raises its caloric value. Chocolate, depending on its type, typically has a high sugar and fat content, contributing further to its caloric density.

In contrast, milk provides not only fewer calories per gram but also offers hydration due to its high water content, making it a lower-calorie option. The balance of macronutrients in milk – with more carbohydrates and less fat compared to the others – allows it to maintain a lower calorific value per gram, making it the correct choice in this context.