Which one among the following has the least coefficient of thermal conductivity?

Thermal conductivity is a measure of a material's ability to transfer heat. It varies significantly across different states of matter. Metals like Copper (Cu) and Aluminum (Al) are excellent conductors because they possess free electrons that facilitate rapid energy transfer; their conductivity values are very high (Cu ≈ 400 W/m·K, Al ≈ 235 W/m·K). Liquids such as Water (H₂O) have much lower conductivity (≈ 0.6 W/m·K) as their molecules are less tightly packed than solids. Gases have the lowest thermal conductivity because their molecules are widely dispersed, leading to infrequent collisions for heat transfer. Among the options provided, Hydrogen (H₂) is a gas and thus has the least coefficient of thermal conductivity (≈ 0.18 W/m·K), despite being high compared to other gases.