Q1: Thermal diffusivity is the most important in heat transfer by

ANS:A - conduction

Thermal diffusivity is most important in heat transfer by conduction. Thermal diffusivity (α) is a material property that describes the rate at which heat diffuses through a substance relative to its ability to store thermal energy. It is defined as the ratio of thermal conductivity (k) to the product of density (ρ) and specific heat capacity (cp​): α=ρ⋅cp​k​ In heat transfer by conduction, heat is transferred through a material by the molecular motion of its particles. Thermal diffusivity plays a critical role in determining how quickly heat can propagate through a material under the influence of a temperature gradient. Materials with higher thermal diffusivity conduct heat more rapidly, while those with lower thermal diffusivity conduct heat more slowly. In contrast, in heat transfer by radiation, condensation, and natural convection, thermal diffusivity has less direct relevance, as these mechanisms involve different modes of heat transfer that are not primarily governed by the ability of a material to conduct heat through molecular motion.