Q1: Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because

ANS:C - radiation becomes important

The correct answer is: c) Radiation becomes important. The Leidenfrost point is the temperature at which a liquid begins to boil so vigorously that it forms a vapor layer between the liquid and a solid surface, effectively reducing heat transfer through conduction. This phenomenon significantly reduces the heat flux at temperatures beyond the Leidenfrost point. However, beyond the Leidenfrost point, as the temperature drop (difference between the liquid temperature and the surface temperature) increases further, other modes of heat transfer, such as radiation, become increasingly important. Radiation becomes significant when there's a considerable temperature difference between the boiling liquid and the surface. As this temperature difference increases beyond the Leidenfrost point, radiation becomes a dominant mode of heat transfer, contributing to the increase in heat flux.