ANS:B - 1

The Prandtl and Reynolds analogy relates the momentum and heat transfer processes in fluid flow. It assumes that the boundary layer thickness for momentum transfer is similar to the boundary layer thickness for thermal transfer. When the Prandtl number (Pr) is equal to 1, the flow is considered to be similar for momentum and thermal transfer. Therefore, the Prandtl and Reynolds analogy is most applicable when the Prandtl number is around 1. So, the correct answer is: 1