Chlorine is used as the disinfectant in a municipal water treatment plant. It achieves $50$ percent of disinfection efficiency measured in terms of killing the indicator microorganisms (E-Coli) in $3$ minutes. The minimum time required to achieve $99$ percent disinfection efficiency would be
- $9.93$ minutes
- $11.93$ minutes
- $19.93$ minutes
- $21.93$ minutes
