The effect of cationic size on the conductivity and viscosity of ionic liquids can be understood by examining the relationship between the size of the cation, the mobility of ions, and the overall properties of the ionic liquid.1. Conductivity: The conductivity of an ionic liquid is primarily determined by the mobility of its ions. In general, smaller cations have higher mobility due to their lower mass and smaller size, which allows them to move more freely through the liquid. As the cationic size increases, the mobility of the ions decreases, leading to a decrease in the overall conductivity of the ionic liquid. This is because larger cations experience greater resistance to movement due to their increased mass and larger size, which can result in stronger interactions with the surrounding anions and solvent molecules.2. Viscosity: The viscosity of an ionic liquid is influenced by the strength of the interactions between its ions and the overall organization of the liquid. Larger cations tend to have stronger interactions with the surrounding anions and solvent molecules due to their increased size and surface area. These stronger interactions can lead to the formation of more structured and organized liquid networks, which can result in higher viscosity. Conversely, smaller cations have weaker interactions with the surrounding anions and solvent molecules, leading to less structured and more fluid liquid networks, which can result in lower viscosity.In summary, the cationic size has a significant effect on the conductivity and viscosity of ionic liquids. As the cationic size increases, the conductivity generally decreases, and the viscosity increases due to the decreased mobility of ions and the stronger interactions between the ions and the surrounding molecules.