Hi Ram Mohan Nayak !

Respiratory quotient is the ratio of the volume of carbon dioxide
produced to the volume of oxygen consumed in respiration over a period
of time.

RQ = Volume of C02 evolved/Volume of 02 absorbed

The Respiratory Quotient value indicates which macronutrients are being
metabolized, as different energy pathways are used for fats,
carbohydrates, and proteins.
If metabolism consists solely of lipids, the Respiratory Quotient is
0.7, for proteins it is 0.8, and for carbohydrates it is 1.0. Most of
the time, however, energy consumption is composed of both fats and
carbohydrates.
And it will be infinity in case of anaerobic conditions.

RQ (Respiratory Quotient) is the ratio of volume of carbon-dioxide evolved to volume of oxygen consumed. 

In anaerobic conditions (like fermentation), volume of oxygen consumed is zero. Hence regardless of the volume of carbon dioxide evolved, the RQ will always be infinte as Volume of carbon dioxide evolved/0 (as no oxygen is utilised) = infinite.