Identify the substances that are likely to dissociate in water. Check all that apply.

From the above options, the best Thermal insulator will be a Plastic cup.

Option (b);

Explanation

Thermal insulators resist to conduct energy or reduction of heat transfer when objects come across in contact with radiation or higher heat object. To conduct energy we need metal or those materials which contain free electrons in it to move from one metal to another.

Plastic doesn't have metallic character so it will resist the heat up to some threshold. Mostly this material is used in separating two current-conducting material. There are many other examples of thermal insulator such as Rubber, fabrics, paper, wood, wool.