155.  The bed slope in slow sand filters, is generally kept
A. 1 in 50
B. 1 in 75
C. 1 in 100
D. 1 : 200.

---

156.  Pick up the incorrect statement from the following :
A. The water entering the slow sand filters should be treated by 9.386 coagulants
B. The depth of water on the filter should be twice the depth of the filter sand
C. When the filter head is 0.75 times the depth of filter sand, the water obtained is purest
D. All the above.

---

157.  In slow sland filters, the turbidity of raw water can be removed only up to
A. 60 mg/litre
B. 75 mg/litre
C. 100 gm/litre
D. ft0 mg/litre.

---

158.  Rapid gravitYfilters
A. were developed by G.W. Fullar
B. inake use of coarser sand with effective size as 0.5 mm yield as high as 30 times the yield of slow sand filters
C. are fed with coagulation treated water
D. all the above.

---

159.  In rapid sand filters the ratio of length and diameter of the lateral, should not be greater than
A.10
B.15
C.20
D.25

---

160.  The best process of disinfection of public water supply, is by
A. boiling
B. chlorination
C. adding lime
D. adding zone.

---

161.  Pick up the correct statement from the following :
A. Due to boiling, the bacterias present in water can be destroyed
B. Lime may be used for softening hard water
C. Excess lime when added to water, raises the pH value of water
D. All the above.

---