In adsorption by activated carbon, which of the following is not a primary factor influencing adsorption?

• A. Color of the water
• B. Chemical nature of the contaminant
• C. pH of the water
• D. Contact time

Answer: (A)

The key idea is that adsorption on activated carbon is driven by how the contaminant molecules interact with the carbon surface and how solution conditions affect those interactions, not by the water’s color. The color itself doesn’t change adsorption capacity or kinetics; it’s just an indicator that colored substances are present. What matters is the chemical nature of the contaminant—its polarity, functional groups, and size—which determine how strongly it will adsorb to the carbon. The pH of the water influences ionization and the surface charge, altering electrostatic attractions or repulsions that can boost or hinder adsorption. Contact time matters because adsorption is a rate process; given more time, more contaminant molecules can diffuse into the carbon pores and approach equilibrium.