At what concentration is the solution strong enough to kill bacteria?

• A. 100 ppm
• B. 200 ppm
• C. 50 ppm
• D. 300 ppm

Answer: (B)

The key idea here is the minimum bactericidal concentration—the lowest level of a disinfectant needed to reliably kill bacteria. At too low a concentration, the agent can’t overwhelm the bacteria’s defenses, so some survive. When the concentration reaches about two hundred parts per million, the antimicrobial is strong enough to damage essential cellular components and disrupt membranes to a lethal extent, leading to bacterial death. That makes two hundred ppm the threshold among the given options that is capable of killing bacteria. Concentrations like fifty or a hundred ppm are below this threshold and unlikely to produce a complete kill, while a higher concentration such as three hundred ppm would certainly kill but isn’t required to meet the “strong enough” criterion in this scenario.