This set of Environmental Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Fluoridation and Defluoridation”.
1. The fluoride concentration for prevention of dental caries is ____________
a) 1mg/l
b) 2mg/l
c) 3mg/l
d) 4mg/l
View Answer
Explanation: Dental caries occurs in children. It can be prevented when the concentration of fluoride in water is between 0.7 to 1.2mg/l.
2. In which process, the fluoride content of water is raised?
a) Chlorination
b) Fluoridation
c) Defluoridation
d) Flocculation
View Answer
Explanation: When the fluoride content is low, it will cause dental caries. So the fluoride content of water is raised and the process is called fluoridation.
3. Which of the following is not used as a fluoride compound?
a) Sodium fluoride
b) Sodium silico fluoride
c) Hydrofluosilicic acid
d) Sodium fluro carbonate
View Answer
Explanation: Sodium fluoride, sodium silico fluoride, hydrofluosilicic acid and sodium fluro carbonate are the fluoride compounds used for fluoridation.
4. Which of the following is the pure compound?
a) Sodium fluoride
b) Sodium silico fluoride
c) Hydrofluosilicic acid
d) Sodium fluro carbonate
View Answer
Explanation: Sodium fluoride is the most purest compound having 95-98% purity due to which, they are commonly used for fluoridation.
5. As far as safer handling is considered, which of the following is used for fluoridation?
a) Sodium fluoride
b) Sodium silico fluoride
c) Hydrofluosilicic acid
d) Sodium fluro carbonate
View Answer
Explanation: For safer handling, hydrofluosilicic acid is preferred as even if it is spilled on the skin, it can be removed easily by washing in cold water.
6. Fluorides in solution form are preferred over powdered form for fluoridation.
a) True
b) False
View Answer
Explanation: Fluorides in powdered form like sodium fluoride or sodium fluosilicate are toxic and must be contained in air tight containers. Hence, they are not preferred.
7. What happens when water contains 8-20 ppm of fluoride concentration?
a) Blue baby disease
b) Crippling fluorosis
c) Dental fluorosis
d) Mottling of teeth
View Answer
Explanation: Dental fluorosis is caused when fluoride concentration is above 3 ppm, whereas Crippling fluorosis is caused when the concentration of fluoride in water is between 8 and 20ppm.
8. The process of reducing the fluoride content from water is called _____
a) Chlorination
b) Fluoridation
c) Defluoridation
d) Flocculation
View Answer
Explanation: When the fluoride content in water is high, it is essential to reduce the fluoride content to avoid health related problems and the process of reducing the fluoride content is called defluoridation.
9. Which of the following is not used for defluoridation?
a) Calcium phosphate
b) Copper sulfate
c) Alum
d) Bone charcoal
View Answer
Explanation: Copper sulfate is used to remove taste, odor, color and control of algae growth and it is not used for fluoridation.
10. At which temperature, the bone is calcinated during defluoridation with calcium phosphate?
a) 100-200oC
b) 200-300oC
c) 400-600oC
d) 500-800oC
View Answer
Explanation: During defluoridation by calcium phosphate, the bone is calcinated at 400-600oC for 10 minutes followed by mineral acid treatment.
11. One cubic metre of bone can treat how much quantity of water containing 3.5 ppm of fluoride?
a) 10m3
b) 100m3
c) 1000m3
d) 10000m3
View Answer
Explanation: Bone is used in the filter for removal of fluorides. One cubic metre of bone can treat 100m3 water containing 3.5 ppm of fluoride.
12. Which material is used in contact filters for the removal of fluorides?
a) Calcium phosphate
b) Copper sulfate
c) Synthetic tri-calcium phosphate
d) Bone charcoal
View Answer
Explanation: Synthetic tri-calcium phosphate is used in contact filters for the removal of fluorides. It is made from the milk of lime and phosphoric acid.
13. Which material is used for removing fluorides from hard water containing 3ppm of fluorides?
a) Lime
b) Copper sulfate
c) Synthetic tri-calcium phosphate
d) Bone charcoal
View Answer
Explanation: Lime is suitable for removing fluorides from hard water containing less than 4ppm. Magnesium is also removed when this material is used for defluoridation.
14. Fluorex is a special mixture of ____________
a) Di-calcium phosphate and carbon
b) Tri-calcium phosphate and hydroxyapatite
c) Di-calcium phosphate and phosphoric acid
d) Tri-calcium phosphate and carbon
View Answer
Explanation: Fluorex is used for removing fluoride and it is a special mixture of tri-calcium phosphate and hydroxyapatite. It is used as a filter medium.
Sanfoundry Global Education & Learning Series – Environmental Engineering.
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