Which of the following is classified as a Thermal Insulator (ऊष्मारोधी)?

Thermal insulators are materials through which no heat conduction takes place at all (or negligibly so). Option A (Water) is incorrect — water is listed as a good conductor of heat in the study material. Water has relatively high thermal conductivity compared to most non-metals and is used as a coolant in engines and nuclear reactors. The human body also contains water and is listed among conductors. Option B (Aluminium) is incorrect — aluminium is a metal and all metals are good conductors of heat. Aluminium is extensively used in heat exchangers, cookware, and aerospace applications due to its high thermal conductivity. Option C (Ebonite) is CORRECT — ebonite (hard vulcanized rubber) is a thermal insulator. The image specifically classifies thermal insulators (ऊष्मारोधी) as materials through which heat conduction does not occur at all. Examples given include ebonite (एबोनाइट) and asbestos (एस्बेस्टस). Ebonite is also an excellent electrical insulator. Option D (Iron) is incorrect — iron is a metal and therefore a good conductor of heat.