Question

R.Q. of malic acid is
A)0.7
B)1
C)1.33
D)4

Answer 1

Hint: RQ is called the respiratory quotient which is defined as the ratio of
$CO_2$ produced to $O_2$ consumed while the food is being metabolized. RQ = $CO_2$ eliminated divided by $O_2$ consumed.

Complete answer:
Most energy sources consist of carbon, hydrogen and oxygen. This includes fat, proteins, carbohydrates and ethanol. Upon their digestion, the ratio of $CO_2$ produced to $O_2$ consumed gives the respiratory quotient. Let us analyze the options to find out the correct option.

Option A: The chemical composition of fats differ from carbohydrates and their metabolism gives a respiratory quotient value of 0.7. Example of this is digestion of palmitic acid. Therefore, this is the incorrect option.

Option B: The RQ of carbohydrates when they undergo aerobic respiration is unity or 1 as the amount of carbon dioxide produced is equal to amount of oxygen consumed. Therefore, this is the incorrect option.

Option C: Malic acid is an organic acid and organic acids have their R.Q. value greater than 1. So, R.Q. = $4CO_2$ divided by $3O_2$ = 1.33. Therefore, this is the correct option.

Option D: RQ of organic acids is greater than unity. RQ for oxalic acids is 4. Therefore, this is the incorrect option.

Hence, the correct answer is option (C)

Note: RQ value is important as it helps in determining respiratory substrate, knowing type of respiration performed, and information of major transformation of food material.