A substance is present in a concentration of 2 mg% in the afferent aeriole and zero mg% in the efferent. True about the substance is:

This is only a hypothetical situation. Filtration fraction is about 20%. It means, of the total plasma passing through the glomerulus per unit time, about 20% is filtered out. If a substance has zero concentration in the efferent aeriole, it means all of that substance was freely and completely filtered out in the plasma that has formed the Glomerular Filtrate.