246.  Bacterias which can survive with or without free oxygen, are known
A. aerobic bacterias -
B. anerobic bacterias
C. facultative bacterias
D. none of these.

---

247.  For complete stabilisation of organic matter in polluted water, it takes
A. 5 days
B. 10 days
C. 20 days
D. 30 days

---

248. For controlling algae, the most commonly used chemical, is
A. copper sulphate
B. alum
C. lime
D. bleaching powder.

---

249.  Chemical coagulation of drinking water, is done
A. to settle suspended materials
B. to increase rate of settlement of suspended materials
C. to remove the bacterias
D. none of these.

---

250.  Disinfection of drinking water, is done to remove
A. odour
B. bacterias
C. turbidity
D. colour.

---

251.  Aeration of water is done to remove
A. odour
B. colour
C. bacterias
D. hardness

---

252.  The flow of water gets retarded, in
A. settling tank
B. sedimentation tank
C. clarifer
D. all the above.

---