To help deep-sea divers breathe, they carry cylinders of oxygen mixed with
- A.chlorine
- B.helium
- C.nitrogen
- D.ozone
Correct answer
Explanation
The correct answer is B, helium. Deep-sea divers breathe a mixture of oxygen and helium because helium does not dissolve much in blood under high pressure.
At great depths the water pressure forces gases from the breathing mix into the blood. Nitrogen, the main gas in ordinary air, dissolves readily and causes nitrogen narcosis, a drunk-like confusion, and on a fast ascent it forms bubbles in the blood, causing the bends (decompression sickness). Helium is inert and far less soluble, so it avoids these problems. The oxygen-helium mix is called heliox.
A is wrong because chlorine is a poisonous gas that damages the lungs.
C is wrong because nitrogen is exactly the gas divers try to avoid at depth, for the reasons above.
D is wrong because ozone is a toxic irritant and is never used in breathing gas.
Exam tip: heliox, oxygen plus helium, protects deep divers from nitrogen narcosis and the bends.
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.
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