11.As compared to higher pH values, the contact period required for efficient chlorination at lower pH values is

12.The rate of Alteration of pressure filters is

13.As compared to cast iron pipes, steel pipes are

14.Period of cleaning of slow sand filters is about

15.Cleaning is done by i) scraping and removal in filters slow sand ii) back washing in slow sand filters iii) scraping and removal in filters rapid sand iv) back washing in rapid sand filters The correct answer is