Which material is NOT typically associated with mutual capacitance?

Mutual capacitance is a concept typically associated with the ability of two conductive objects to store electrical energy when separated by an insulating material. In this context, air, insulating materials, electrical conductors, and liquid dielectrics can all play a role in how mutual capacitance is exhibited. However, air, while it can act as a dielectric, is not used in a manner that's typically associated with mutual capacitance in practical applications.

Electrical conductors are essential in forming the plates of capacitors, while insulating materials are needed to separate these conductors and allow for capacitance to occur. Liquid dielectrics can also be used in certain capacitor designs to enhance the capacitance effect. Therefore, air is less directly associated with mutual capacitance compared to the other materials listed, making it the least fitting answer in this context.