274. The maximum permitted loss of head in a rapid sand filter, is
A. 1 m
B. 2 m
C. 3 m
D. 4 m

---

275.  In a rapid sand filter, air binding is caused due to excessive
A. negative pressure
B. pressure
C. turbidity
D. water pressure

---

276.  Mud balls may be removed by
A. breaking and washing
B. washing the filter with a solution of caustic soda
C. removing, cleaning and replacing the damaged sand
D. all the above,

---

277.  Rapid gravity filters can remove bacterial impurities up to a maximum of
A.50%
B.60%
C.70%
D.80%

---

278.  Rapid gravity filter can only remove turbidity of water upto
A. 15 to 25 gm/litre
B. 25 to 30 gm/litre
C. 30 to 35 cm/litre
D. 35 to 40 gm/litre

---

279.  E. Coli bacterias die in water having pH greater than
A.5.5
B.6.5
C.7.5
D. 9.5.

---

280.  The most ideal disinfectant used for drinking water throughout the world, is
A. alum
B. lime
C. chlorine
D. nitrogen

---