SOLUTION

Solvation, commonly called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute.
For conduction we require free ions,due to solvation free ions in the solution are reduced hence is the conduction.

ya,u r right.as solvation of ions increases,the free ions get surrounded by d solvent molecules,which reduces their free nature,resulting in d decrease of conductance