ANS:B - on rough surfaces

Nucleate boiling is typically promoted on rough surfaces. Here's why:

1. Surface Roughness: Nucleation sites, where bubbles form during nucleate boiling, are often found on rough surfaces. Irregularities on the surface provide cavities or crevices where vapor bubbles can form more easily due to local pressure variations. These nucleation sites enhance the initiation and growth of bubbles, promoting nucleate boiling.
2. Enhanced Nucleation: Surface roughness increases the surface area available for nucleation, which facilitates the formation of vapor bubbles. In contrast, smooth or polished surfaces have fewer nucleation sites, making it more difficult for bubbles to form.
3. Agitation: While agitation can influence boiling behavior by enhancing mixing and promoting convective heat transfer, it is not a primary factor in promoting nucleate boiling. Nucleate boiling can occur with or without agitation, but surface roughness plays a more significant role in promoting bubble formation.