What is the primary role of an activity coefficient in a solution?

If the concentration of a solute is 0.5 M and its activity coefficient is 0.8, what is the activity of the solute?

What is the formula for calculating ionic strength (μ) of a solution?

For the dissolution of AgCl in water, how would you express the K_sp using activity coefficients?

How does the extended Debye-Hückel equation account for ionic size in calculating activity coefficients?