ANS:A - Iron

Among the options provided, iron has the maximum thermal conductivity. Thermal conductivity is a measure of a material's ability to conduct heat. Generally, metals have higher thermal conductivity compared to non-metals. Iron, being a metal, exhibits high thermal conductivity due to the mobility of its free electrons, which allows heat to be transferred rapidly through the material. On the other hand, coal, nitrogen, and tar are non-metals and typically have lower thermal conductivity compared to metals like iron. Therefore, among the options provided, iron would have the maximum thermal conductivity.