The changes in conductivity for metallic conductors and semiconductors when they are heated can be understood by examining their electronic properties and how these properties respond to temperature changes: Metallic Conductors: In metallic conductors, conductivity depends largely on the movement of free electrons. As temperature increases, the metal's atomic lattice vibrates more vigorously, causing more frequent collisions between free electrons and the lattice atoms. These increased collisions impede electron flow, thereby decreasing the metal's conductivity. Thus, the conductivity of metallic conductors decreases with an increase in temperature. Semiconductors: Semiconductors, on the other hand, behave differently. Their conductivity is highly sensitive to temperature changes. At low temperatures, semiconductors have few charge carriers because their electrons are bound closely to atoms. As the temperature rises, more electrons gain enough thermal energy to jump from the valence band to the conduction band, creating electron-hole pairs and thereby increasing the number of charge carriers available for conduction. As a result, the conductivity of semiconductors increases with an increase in temperature. To summarize: Metallic Conductors: Conductivity decreases with an increase in temperature. Semiconductors: Conductivity increases with an increase in temperature. Therefore, the correct answer is: Option D: decrease, increase