Read the passage carefully and answer the questions.

The resistance (R) of an object is given by the expression $ρ\frac{l}{A}$. The inverse of R is called conductance and the inverse of $ρ$ is called conductivity or specific conductance represented by K. The conductivity depends upon the nature of the material (insulator, semiconductor or conductor) and the temperature of the substance. Similarly, the conductance due to the ions present in the solution (ionic conductance) depends upon the nature of the electrolyte, size of the ions produced, the nature of the solvent and the temperature. Molar conductivity ($Λ_m$) of a solution at a given concentration is the conductance of the volume V of solution containing one mole of electrolyte kept between two electrodes with area of cross-section A and the distance of unit length. It is given by the expression, $Λ_m = kV$. Molar conductivity increases with the decrease in concentration and when the concentration approaches zero, it is called limiting molar conductivity. The decrease is linear in the case of a strong electrolyte. However, in the case of a weak electrolyte, the change in molar conductivity is gradual in the higher concentration range and there is a sharp increase in molar conductivity as the concentration approaches zero. From the limiting molar conductivity values of a strong electrolyte, we can find the limiting molar conductivity of a weak electrolyte containing the common ions using the Kohlrausch law of independent migration of ions. From molar conductivity and limiting molar conductivity, we can Am determine the degree of dissociation ($\frac{Λ_m}{Λ_m^o}$) and ionization constant of a weak acid.

Which of the following is an insulator?

Teflon

The correct answer is Option (2) → Teflon

Materials can be classified based on their ability to conduct electricity into conductors, semiconductors, and insulators.

• Conductors allow the free flow of electrons.

• Semiconductors conduct electricity moderately.

• Insulators do not allow the flow of electric current because they lack free electrons.

Graphite Graphite conducts electricity due to the presence of delocalized electrons within its layered structure. Therefore, it behaves as a conductor, not an insulator.

Teflon Teflon (polytetrafluoroethylene, PTFE) is a polymer with very strong covalent bonds and no free electrons. Because of this, it does not conduct electricity and acts as an excellent electrical insulator.

Germanium Germanium is a semiconductor commonly used in electronic devices such as diodes and transistors. Hence it is not an insulator.

Sodium Sodium is a metal, and metals conduct electricity due to the presence of free mobile electrons. Therefore sodium is a conductor.