Deficiency of fluoride leads to which one of the following health problems?
- A.Tooth caries
- B.Mottling of tooth
- C.Bending of bones
- D.Stiffening of joints
Correct answer
Explanation
The correct answer is A, Tooth caries. Too little fluoride weakens tooth enamel and makes teeth prone to decay, known as dental caries.
Fluoride becomes part of the enamel as fluorapatite, which resists the acids made by mouth bacteria from sugars. This is why fluoride is added to toothpaste and, in some countries, to drinking water. The safe level in drinking water is about 1 mg per litre; India's standard allows up to 1.5 mg per litre. Too much fluoride is also harmful and causes fluorosis, a serious problem in parts of Rajasthan, Andhra Pradesh and Telangana.
B is wrong: mottling of teeth (dental fluorosis) is caused by an excess of fluoride, not a deficiency.
C is wrong: bending of bones results from skeletal fluorosis, again due to excess fluoride.
D is wrong: stiffening of joints is also a sign of skeletal fluorosis from too much fluoride.
Exam tip: fluoride too little = dental caries; fluoride too much = fluorosis (mottled teeth, bent bones, stiff joints).
Practice Questions
View allBronze is an alloy of copper and
- A.nickel
- B.iron
- C.tin
- D.aluminium
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Bronze is an alloy of copper and tin, usually about 88 parts copper to 12 parts tin. Adding tin makes copper harder, stronger and easier to cast, and bronze also resists corrosion well.
Read the full explanation →Which one of the following instruments is used for measuring moisture content of air?
- A.Hydrometer
- B.Hygrometer
- C.Hypsometer
- D.Pycnometer
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A hygrometer measures humidity, that is, the amount of water vapour or moisture in the air. The name comes from the Greek "hygros", meaning wet.
Read the full explanation →Which one of the following elements is present in the green pigment of leaves?
- A.Magnesium
- B.Iron
- C.Calcium
- D.Copper
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The green pigment of leaves is chlorophyll, and a magnesium atom sits at the centre of every chlorophyll molecule.
Read the full explanation →Consider the following actions :
1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode
In how many of the above actions is the function of accelerometer required?
- A.Only one
- B.Only two
- C.All three
- D.None
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An accelerometer measures acceleration, including the pull of gravity, and each of the three actions depends on reading it. An accelerometer is a small sensor, today usually a MEMS (micro-electro-mechanical system) chip, that senses changes in speed and the direction of gravity.
Read the full explanation →Consider the following statements :
1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.
Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Carbon fibre is widely used in cars and aircraft for its strength and low weight, and it can be recovered and recycled.
Read the full explanation →