The food that provides the most energy per gram is (b) Fat. Fat is the most energy-dense macronutrient, providing 9 calories per gram, whereas protein and carbohydrate each provide 4 calories per gram.

This high energy density of fats makes them valuable energy reserves in the body, providing a concentrated source of fuel for metabolic processes, physical activity, and overall energy balance. While protein and carbohydrate also contribute to energy metabolism, they are less energy-dense compared to fats.

Although vitamins (d) play crucial roles in various physiological processes within the body, they do not provide energy in the same way as macronutrients like fat, protein, and carbohydrate. Instead, vitamins function as essential micronutrients that support metabolism, immune function, and overall health, but they do not yield calories when metabolized.