The correct option is Silver and copper.
Explanation
Metals are generally good conductors of heat due to the presence of free electrons which facilitate the rapid transfer of energy. However, the efficiency of thermal conduction varies significantly across different metals based on their atomic structure.
Analysis of Conductivity:
- Silver (Ag): It has the highest thermal conductivity of all metals.
- Copper (Cu): It ranks second to silver in thermal conductivity. Because it is much cheaper than silver, it is extensively used in industrial applications like heat exchangers and cooking utensils.
- Aluminium (Al): While it is a good conductor of heat, its conductivity is lower than that of silver and copper.
- Poor Conductors: Lead (Pb) and Mercury (Hg) are comparatively poor conductors of heat among metals.
Therefore, the pair consisting of Silver and Copper represents the best conductors of heat.
Key Takeaway: Silver is the best conductor of heat followed by copper, whereas lead and mercury are poor conductors of heat.