Carbohydrate catabolism yields ____________ cal/g.

Carbohydrate catabolism primarily refers to the metabolic processes that break down carbohydrates to release energy. The energy yield from the complete oxidation of carbohydrates, such as glucose, is approximately 4 kilocalories per gram. This value is widely accepted in biochemistry and nutrition, reflecting the amount of energy available for use by the body after carbohydrates are metabolized through pathways such as glycolysis and the citric acid cycle.

The lower energy yield compared to fats and proteins can be attributed to the chemical structure of carbohydrates, particularly their content of carbon, hydrogen, and oxygen, and the specific metabolic pathways involved in breaking them down. When carbohydrates are fully oxidized, they produce carbon dioxide and water as byproducts, allowing the release of energy stored in their chemical bonds.

Looking at the other options, 5, 6, and 7 cal/g would overestimate the energy content derived from carbohydrates, as these figures do not align with the established values for carbohydrate metabolism. Hence, the accepted figure of around 4 cal/g for carbohydrate catabolism is the accurate representation of the energy yield from this macronutrient.