At very low temperature, lead (Pb) shows a special electrical behaviour. At such low temperatures, lead behaves as which of the following types of materials?

Introduction / Context:
The electrical properties of materials can change dramatically with temperature. At room temperature, metals such as copper, aluminium, and lead are good conductors, while insulators and semiconductors behave differently. However, at very low temperatures, certain metals undergo a remarkable transition to a superconducting state, in which their electrical resistance drops to nearly zero. This question asks specifically about lead and its behaviour at low temperatures, testing your awareness of superconductivity in basic physics and chemistry.

Given Data / Assumptions:

• The material in question is lead, a heavy metal with symbol Pb.
• The context is behaviour at low temperature, not at room temperature.
• The options include semiconductor, superconductor, insulator, and conductor.
• We assume the concept of superconductivity as understood in school level physics.

Concept / Approach:
At ordinary temperatures, lead behaves like a normal metal and is a good conductor, though not as good as copper or silver. However, when cooled below a certain critical temperature (a few kelvin), lead undergoes a transition to a superconducting state. In this state, its electrical resistance becomes essentially zero and it can conduct current without energy loss. This phenomenon is called superconductivity and is observed in several elemental metals and many alloys. In contrast, semiconductors like silicon behave differently, insulators do not conduct at all, and ordinary conductors still have some resistance at all practical temperatures. Therefore, the special low temperature behaviour of lead corresponds to it becoming a superconductor.

Step-by-Step Solution:
Step 1: Recall the normal behaviour of lead at room temperature. Lead is a metal and thus a good electrical conductor under normal conditions. Step 2: Consider what happens at very low temperatures. Some metals, including lead, transition into a superconducting state when cooled below a critical temperature. Step 3: Understand the meaning of “superconductor”. A superconductor has practically zero electrical resistance and can maintain persistent currents without energy loss. Step 4: Match this behaviour with the given options and select “Super conductor”.

Verification / Alternative check:
Lists of elemental superconductors in standard physics references include metals such as lead, mercury, and tin that become superconducting at temperatures near absolute zero. Each has a specific critical temperature below which superconductivity appears. Experimental data on lead show that at such low temperatures, its resistivity drops sharply to near zero and it exhibits the Meissner effect (expulsion of magnetic fields), confirming its superconducting nature. In contrast, semiconductors like silicon or germanium become less conductive as temperature falls, and insulators never become perfect conductors. This evidence supports the conclusion that low temperature lead behaves as a superconductor.

Why Other Options Are Wrong:
Option A (Semi conductor): Lead is not a semiconductor; its electronic structure and behaviour at room temperature clearly identify it as a metal. Option C (Insulator): Lead does not become an insulator at low temperature; on the contrary, its resistance drops dramatically. Option D (Conductor): While lead is a conductor at room temperature, the question emphasises the special behaviour at low temperatures, which is more specific than simply “conductor”.

Common Pitfalls:
Students sometimes think that all materials simply become better conductors as they are cooled, forgetting the special phenomenon of superconductivity. Others may confuse semiconductors with metals and assume that any temperature-dependent behaviour must be semiconductor-like. To avoid such confusion, remember that some metals, including lead, exhibit a unique phase transition into a superconducting state at very low temperatures, characterised by zero resistance and perfect diamagnetism.

Final Answer:
At low temperature, lead behaves as a Super conductor.