Ans. C: 5 ppm Park's PSM, 21st ed., p- 723 states: Chlorine destroys cyclops and larvae of the guineaworm in a strength of 5 ppm Cyclops may be controlled by the use of the physical, chemical or biological methods: Physical methods - Straining - Boiling at 60 degree Celsius Chemical methods - Chlorine in a strength of 5 ppm - Lime - Abate Biological - Barbel fish and gambusia fish The most satisfactory and permanent method of controlling Cyclops in drinking water is to provide piped water supply or tube wells. Abolition of step wells and provision of sanitary wells should receive attention in rural areas.