A centrifugal pump running at 500 rpm and at its maximum efficiency is delivering a head of 30 m at a flow rate of 60 L/min. If the rpm is changed to 1000, then the head ‘H’ in meter and flow rate ‘Q’ in L/min at maximum efficiency is estimated to be

• A. H = 60, Q = 120
• B. H = 120, Q = 120
• C. H = 60, Q = 480
• D. H = 120, Q = 30