Discharge of a centrifugal pump is
A. Directly proportional to diameter of its impeller
B. Inversely proportional to diameter of its impeller
C. Directly proportional to (diameter)2 of its impeller
D. Inversely proportional to (diameter)2 of its impeller
Answer: Option D

Option c is correct..
Q=A.V=pi.d^2/4.v
C. Directly proportional to (diameter)² of its impeller
Ans should be c.
Discharge of centrifugal pump is Q = area* velocity of flow.
Q = (pi)(D1)(B1)(VF1) = (PI)(D2)(B2)(VF2).
Where B1 and B2 are width of impeller at inlet and outlet and B1 and B2 are diameter of impeller at inlet and outlet and VF1 and VF2 are velocity of flow at inlet and outlet.
The discharge flow rate of a centrifugal pump is directly proportional to diameter. Discharge head is directly proportional to the square of the diameter. And power is directly proportional to the cube of the diameter. You can understand all this with the help of affinity laws.
The right answer is C
Option A is the right one as Q= pi*D*B*Vf is the equation for discharge