Molar conductivity of ______ increases drastically on dilution.

\(CH_3COOH\)

The correct answer is option 3. \(CH_3COOH\).

Molar conductivity measures the electrical conductivity of a solution relative to its concentration. As the concentration of an electrolyte increases, ion-ion interactions hinder their movement, decreasing the molar conductivity. However, dilution reduces these interactions, allowing ions to move more freely and conduct electricity more efficiently.

In the case of CH₃COOH, it acts as a weak acid in aqueous solution, partially dissociating into CH₃COO⁻ and H⁺ ions: CH₃COOH ⇌ CH₃COO⁻ + H⁺.

When you dilute a CH₃COOH solution, the increase in water molecules provides more space for the existing ions to move around. This reduces the collisions between ions, leading to a significant increase in their mobility and, consequently, the molar conductivity.

Compared to CH₃COOH, NH₄Cl, NaCl, and CH₃COONa are strong electrolytes and already dissociate completely in aqueous solutions. Dilution doesn't significantly impact their ionization, and their molar conductivity increases only gradually due to reduced ion-ion interaction.

Therefore, only CH₃COOH exhibits a dramatic increase in molar conductivity on dilution due to its partial dissociation and enhanced ion mobility with increased water content.