Final answer:
Isopropyl alcohol is most effective as a germicidal agent when used in a 70% aqueous solution. The presence of water in the solution aids in the coagulation of proteins and allows for better penetration of cells, making it more effective at inhibiting microbial growth.
Step-by-step explanation:
Isopropyl alcohol is most effective as a germicidal agent when used in aqueous solution at a concentration of 70%. Alcohols, including isopropyl alcohol, work by denaturing proteins and disrupting membranes, leading to cell lysis. A 70% aqueous solution of isopropyl alcohol is more effective in inhibiting microbial growth than a 100% solution because the presence of water aids in the coagulation of proteins and allows for better penetration of cells.