The correct option is
D Protein
R.Q. is the ratio of amount of CO
2 produced to the amount of O
2 consumed by the cell for respiration. R.Q. value of protein is 0.8 as the volume of carbon dioxide released is less than the amount of oxygen. Carbohydrates, organic acid and starch have R.Q. of 1 or greater than 1.
So, the correct answer is 'Protein'.