Final answer:
The correct unit used to measure the energy from food is the calorie, specifically referred to as the nutritional Calorie or kilocalorie when discussing nutrition.
Step-by-step explanation:
The unit of measurement used to quantify the amount of energy we obtain from a particular food is the calorie. In nutrition, this is often referred to as the nutritional Calorie, or Calorie with a capital 'C', which is equivalent to 1 kilocalorie (kcal). This means that 1 Calorie is the amount of energy needed to raise 1 kilogram of water by 1 degree Celsius. Consequently, the correct answer to the student's question is option 4) calorie.
When considering the energy density in foods, Calories are used to express the amount of energy a food will provide when consumed. This provides an important measure for understanding how different foods contribute to our daily energy needs and how they may impact our health.