- The mobility of ions in water is influenced by their size and hydration energy. Smaller ions tend to have higher mobility because they can move more easily through the solvent.
- Li+ is the smallest ion in this group and has the highest hydration energy, which reduces its mobility.
- K+ has the largest ionic radius and, thus, the lowest mobility among these ions.
Thus, the correct order of mobility is:
\(Li^+ < Na^+ < Ag^+ < K^+\)
Therefore, the correct answer is (D)