The ratio of hydrogen (H) and oxygen (O) in water molecule by volume is

What is the fourth step of raw water treatment?

A. sedimentation

B. coagulation

C. filtration

D. chlorination

The hardness that cannot be removed by boiling is called

A. temporary hardness

B. permanent hardness

C. semi temporary hardness

D. semi permanent hardness

The density of water becomes maximum at

A. 10 °C

B. 4 °C

C. 5 °C

D. 12 °C

Step of sewage water treatment in which sewage is placed in tanks and aerated with large blowers is called

A. primary sewage treatment

B. secondary sewage treatment

C. activated sludge treatment

D. chlorination

What percentage of fresh water is available to man?

A. 0.2

B. 0.02

C. 0.002

D. 0.0002