Which of the following is/are poor conductor(s) of heat?

All of these

The correct answer is option 4. All of these.

The ability of a material to conduct heat is characterized by its thermal conductivity. In the context of the question, poor conductors of heat, or insulators, have lower thermal conductivity values. Let's briefly explain the behavior of the mentioned substances:

1. Air:  Gases have low thermal conductivity because their molecules are widely spaced. Air is a poor conductor of heat, contributing to its insulating properties.

2. Water: Liquids, including water, generally have lower thermal conductivity than metals. Water's ability to retain heat is one reason why it is used as a coolant in various applications.

3. Wood: Wood is an insulator because its structure includes air pockets and fibers that impede the flow of heat. The cellulose and lignin components in wood contribute to its thermal insulating properties.

In practical terms, materials with low thermal conductivity are often used as insulating materials to reduce heat transfer, whether to keep things warm (as in the case of thermal insulation in buildings) or to keep things cool (as in the case of insulating materials for handling low-temperature substances).