Li+(aq):
Lithium readily reacts vigorously with halogens to form ionic halides.
2Li+Cl2→2LiCl
Lithium ion has highest hydrated size among the ions and highest hydration energy among the cations.
It has lowest ionic mobility among the ions.
Na+(aq):
Sodium readily react vigorously with halogens to from ionic halides.
2Na+Cl2→2NaCl
K+(aq):
Potassium readily reacts vigorously with halogens to form ionic halides.
2K+Cl2→2KCl
Rb+(aq):
Rubidium readily reacts vigorously with halogens to form ionic halides.
2Rb+Cl2→2RbCl
It has highest ionic mobility among the ions.