6. Hardness of water does not

A. have any bad effect in boiler
B. make cooking of foods difficult
C. make it unfit for drinking
D. cause difficulty in the washing of clothes with soaps

7. Permanent hard water may be softened by passing it through

A. sodium silicate
B. sodium bicarbonate
C. sodium hexametaphosphate
D. sodium phosphate

8. Zeolite used in the zeolite softening process for the treatment of hard water gets exhausted after certain time of usage but can be regenerated by flushing it with

A. 10% calcium chloride solution
B. 10% magnesium sulfate solution
C. 10% magnesium chloride solution
D. 10% sodium chloride solution

9. Temporary hardness of water is caused by the presence of

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

10. Secondary treatment uses __________ to consume wastes.

A. micro-organisms
B. chemicals
C. filtration
D. none of these