11. Application of quaternary ammonium compounds as sanitizing agents tends to

A. favor gram-positive bacteria
B. decrease gram-positive bacteria
C. increase the percentage of gram(-)ve rods on utensils
D. none of the above

12. Permanent hardness of water is caused by the presence of

A. bicarbonates of calcium and magnesium
B. carbonates of sodium and potassium
C. chlorides and sulfates of calcium and magnesium
D. phosphates of sodium and potassium

13. According to BIS the maximum permissible limit of dissolved solids in drinking water is

A. 1000 mg/l
B. 500 mg/l
C. 2000 mg/l
D. 1500 mg/l

14. Acid used mostly for removal of milk stone is

A. phosphoric acid
B. nitric acid
C. gluconic acid
D. tartaric acid

15. Which of the following chemical is sometimes added in the process of coagulation and flocculation?

A. Aluminum sulfate
B. Aluminum oxide
C. Calcium chloride
D. None of these