Explanation:

A centrifugal pump works on the principle of converting mechanical energy into hydraulic energy. This is accomplished by accelerating the fluid in the impeller and converting the velocity energy into pressure energy as the fluid flows through the volute casing. The pressure rise in the impeller is caused by the centrifugal force generated by the high-speed rotation of the impeller.

The pressure rise in the impeller is measured in terms of head, which is the height of a column of water that would produce the same pressure. There are four types of heads associated with a centrifugal pump: kinetic head, manometric head, static head, and velocity head.

- Kinetic head: The kinetic head is the energy per unit weight of fluid due to its motion. It is given by the formula (V^2/2g), where V is the velocity of the fluid and g is the acceleration due to gravity. The kinetic head is not relevant for determining the starting of a centrifugal pump.
- Manometric head: The manometric head is the energy per unit weight of fluid due to its pressure. It is given by the formula (P/ρg), where P is the pressure of the fluid, ρ is the density of the fluid, and g is the acceleration due to gravity. The manometric head is the head that is required to overcome the losses due to friction and elevation in the system. A centrifugal pump will start delivering water only when the pressure rise in the impeller is equal to or greater than the manometric head.
- Static head: The static head is the energy per unit weight of fluid due to its elevation. It is given by the formula (h), where h is the height of the fluid above a reference point. The static head is the head that is required to lift the fluid from the source to the pump.
- Velocity head: The velocity head is the energy per unit weight of fluid due to its velocity. It is given by the formula (V^2/2g), where V is the velocity of the fluid and g is the acceleration due to gravity. The velocity head is the head that is required to overcome the kinetic energy of the fluid.

Conclusion:

Hence, we can conclude that the correct answer is option B, i.e., manometric head. A centrifugal pump will start delivering water only when the pressure rise in the impeller is equal to or greater than the manometric head.