Explanation

In anaerobic respiration $CO_{2}$ is evolved but oxygen is not used. Therefore in such case respiratory quotient will be infinite. $e.g.,$ $C_{6}H_{12}O_{6}\overset{\ \ Zymase\ \ \ }{\rightarrow}2\ C_{2}H_{5}OH + 2\ CO_{2} +$ Energy Glucose Where, respiratory quotient $= \frac{\ \ \ Evolved\ CO_{2\ \ \ }}{Consumed\ O_{2}}$ $= \frac{2\ CO_{2}}{0\ O_{2}} = \infty(Infinity)$