How do the effective radius, hydration number and activity coefficient of an ion in a solution affect the reaction activity of that ion? Explain.

The effective radius.

For smaller, more highly charged ions, the effective radius is greater than it is for bigger, less highly charged ions. ... Next the activity coefficient of an ion approaches a value of one as the ionic strength approaches zero. The activity of an ion and its concentration are equal in a solution where μ = 0.

Hydration number

They attract and retain several water dipoles around them as ions are dissolved in water.The resolution of this apparent paradox lies in the interaction of water or other polar solvents between ions and molecules. A dipolar water molecule's negative (oxygen) side attracts and is attracted by every positive ion in the solution. Water molecules cluster around positive ions owing to this ion-dipole power. Similarly, negative ions are drawn to the positive hydrogen) ends of water molecules.

Activity coefficient 

As the ion charge increases, the hydrated ionic radius decreases and as the ionic strength of the solution increases, a close look at the Debeye-Hückel equation shows that γ decreases. The effect of ionic strength on the coefficient of activity depends strongly on the charge of the ion.