Assertion (A) : The respiratory Quotient (RQ) depends on the type of respiratory substrate used in metabolism

Reason (R) : Different respiratory substrates such as carbohydrates, proteins, and fats yield different amounts of carbon dioxide $\left(C{O}_2\right)$ and water $\left(H_{2}O\right)$ for the same amount of oxygen $\left(O_2\right)$ consumed, there by affecting the RQ value.
Choose the correct option :

The assertion is true. The respiratory quotient (RQ) is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration. Different respiratory substrates, such as carbohydrates, proteins, and fats, undergo metabolism via different biochemical pathways, yielding varying amounts of carbon dioxide (CO₂) and water (H₂O) for the same amount of oxygen consumed. Therefore, the type of respiratory substrate used affects the RQ value.

Reason (R) is also true. Carbohydrates generally have an RQ close to 1 (producing equal amounts of CO₂ and O₂), while fats have an RQ lower than 1 (producing more CO₂ per O₂ consumed), and proteins may have variable RQ values depending on their composition. Therefore, the nature of the respiratory substrate directly influences the ratio of CO₂ to O₂, determining the RQ.

The Reason (R) provides an explanation for why Assertion (A) is true. Different respiratory substrates indeed yield different amounts of CO₂ and H₂O per unit of O₂ consumed, influencing the RQ value. Thus, both statements are correct and logically connected.