Cash reserve Ratio (CRR) is the amount of funds that the banks have to keep with the RBI. If the central bank decides to increase the CRR, the available amount with the banks comes down. The RBI uses the CRR to drain out excessive money from the system. Scheduled banks are required to maintain with the RBI an average cash balance, the amount of which shall not be less than 4% of the total of the Net Demand and Time Liabilities (NDTL), on a fortnightly basis.
It is fluctuating in nature so generally they don't ask this kind of question.