ANS:A - 7

The Prandtl number (Pr) for water at 20°C is approximately 7. The Prandtl number is defined as the ratio of momentum diffusivity (kinematic viscosity) to thermal diffusivity. For water at 20°C, the kinematic viscosity is around 1.002×10−6 m2/s1.002×10−6m2/s, and the thermal diffusivity is around 1.43×10−7 m2/s1.43×10−7m2/s. Therefore, Prandtl number (Pr) for water at 20°C can be calculated as: Pr=kinematic viscositythermal diffusivityPr=thermal diffusivitykinematic viscosity​ Pr=1.002×10−61.43×10−7≈7Pr=1.43×10−71.002×10−6​≈7 So, the Prandtl number for water at 20°C is about 7.