ANS:A - less than the vapour pressure of the liquid at that temperature.

Cavitation occurs in a centrifugal pump when the suction pressure is less than the vapor pressure of the liquid at that temperature.

Explanation:

1. Vapor Pressure:
   • Vapor pressure is the pressure at which a liquid vaporizes at a given temperature. It is characteristic of the liquid and varies with temperature.
   • When the suction pressure at the inlet of the centrifugal pump drops below the vapor pressure of the liquid being pumped, the liquid starts to vaporize and form vapor bubbles.
2. Cavitation:
   • Cavitation is the formation and collapse of vapor bubbles within a liquid flow due to pressure fluctuations. When these vapor bubbles collapse, they can cause damage to pump components and reduce pump efficiency.
   • Cavitation typically occurs at low-pressure regions within the pump, such as near the impeller blades or in the volute, where the pressure drops below the vapor pressure.
3. Suction Pressure:
   • In a centrifugal pump, the suction pressure is critical because it determines the net positive suction head (NPSH), which should be sufficient to prevent cavitation.
   • If the suction pressure is less than the vapor pressure of the liquid, cavitation will occur because the liquid cannot remain in its liquid state; instead, it vaporizes.
4. Other Options:
   • Suction pressure greater than or equal to the vapor pressure would not lead to cavitation because the liquid remains in its liquid state.
   • Equal to the developed head is unrelated to the conditions that cause cavitation.

Conclusion: