Statement I: The conductivity of metals decreases while that of electrolytic solution increases with — Electrochemistry Chemistry Question

💡 Solution & Explanation

Step 1 - Evaluate Statement I (Temperature Dependence of Metallic and Electrolytic Conductivity) To evaluate Statement I, we must look at the distinct physical mechanisms of electrical conduction in metals and in electrolytic solutions: * **Metallic (Electronic) Conduction:** In metals, charge is carried by highly mobile valence electrons moving through a crystal lattice of positively charged metal ions (kernels). As the temperature ($T$) of the metal increases, the thermal energy causes these positive kernels to vibrate with increasingly larger amplitudes about their mean equilibrium positions. This vigorous lattice vibration acts as a major obstacle to the orderly drift of conduction electrons. The moving electrons undergo more frequent collisions with the vibrating kernels, which scatters them and significantly increases the electrical resistance ($R$). Since electrical conductivity ($\kappa$) is the reciprocal of resistivity ($\rho$), the **conductivity of metals decreases with an increase in temperature**: $$T \uparrow \implies \text{Lattice Vibrations} \uparrow \implies \text{Scattering of } e^- \uparrow \implies R \uparrow \implies \text{Metallic Conductivity} \downarrow$$ * **Electrolytic (Ionic) Conduction:** In electrolytic solutions, electrical current is carried by the physical migration of solvated cations and anions toward their respective electrodes. When the temperature ($T$) of the electrolytic solution increases: 1. The kinetic energy of the ions increases, raising their individual velocities and ionic mobilities ($\mu$). 2. The viscosity ($\eta$) of the solvent decreases, which drastically reduces the frictional drag forces opposing ionic movement. 3. The degree of dissociation ($\alpha$) of weak electrolytes increases, and the inter-ionic attractive forces in strong electrolytes are weakened, producing more freely migrating ions. Consequently, the **conductivity of electrolytic solutions increases with an increase in temperature**: $$T \uparrow \implies \eta \downarrow \text{ and } \text{Kinetic Energy} \uparrow \implies \text{Ionic Mobility } (\mu) \uparrow \implies \text{Electrolytic Conductivity} \uparrow$$ Thus, Statement I is **correct**. Step 2 - Evaluate Statement II (Nature of Electrons in Metals) According to the modern Drude-Lorentz classical "electron-sea" model of metallic bonding: * Metals consist of a rigid, three-dimensional lattice of positively charged metal cores (kernels) immersed in a dense, highly delocalized "sea" of valence electrons. * The valence electrons are **very loosely held** by the atomic nuclei and are completely free to migrate throughout the entire boundaries of the metal specimen under an applied electric field. * If the valence electrons were very tightly held by the nuclei and were not free to move, metals would behave as electrical insulators rather than conductors. Thus, Statement II is **incorrect (false)**. Step 3 - Determine the Correct Option * Statement I is correct. * Statement II is incorrect. * Therefore, the correct choice is Option (C). $$\text{Correct Option: } \boxed{C}$$