Permanent hardness of water may be removed by the addition of
Answer: A
Permanent hardness is removed by adding washing soda, sodium carbonate.
It precipitates the calcium and magnesium as insoluble carbonates:
\[ \mathrm{CaSO_4 + Na_2CO_3 \rightarrow CaCO_3 \downarrow + Na_2SO_4} \]
Boiling removes only temporary hardness, which is due to bicarbonates.
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The confirmatory test for HIV virus causing AIDS is:
Answer: B
The Western blot is the confirmatory test for HIV. It separates viral proteins by electrophoresis and detects antibodies to specific ones, so a positive result is highly specific.
The ELISA is the screening test: it is very sensitive and cheap, but gives false positives, so every reactive ELISA is confirmed by Western blot before a diagnosis is made.
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Air is a/an?
Answer: B
Air is a mixture, not a compound. Its constituents are not combined in any fixed proportion and retain their own properties.
It is about 78 per cent nitrogen, 21 per cent oxygen and 0.93 per cent argon, with carbon dioxide, water vapour and traces of other gases. Each can be separated by physical means, by fractional distillation of liquid air.
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Epoxy resins is used as?
Answer: D
Epoxy resins are used as adhesives, and also as coatings and casting materials.
They are supplied as two parts - resin and hardener - that cross-link on mixing into a rigid solid, bonding strongly to metal, glass and ceramics.
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Newton is the unit of:
Answer: A
The newton is the SI unit of force - the force that gives a mass of one kilogram an acceleration of one metre per second squared:
\[ 1\ \mathrm{N} = 1\ \mathrm{kg\,m/s^2} \]
An apple of about 100 g weighs roughly one newton, which is the origin of the familiar story.
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The most important ore of aluminum is
Answer: D
Bauxite is the chief ore of aluminium, a mixture of hydrated aluminium oxides.
The oxide is extracted from it by the Bayer process and then reduced to the metal by electrolysis in molten cryolite. Calamine is a zinc ore, calcite calcium carbonate, and galena lead sulphide.
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The weight of an object will be minimum when it is placed at?
Answer: D
An object weighs least at the centre of the earth, where it weighs nothing at all.
There the mass of the earth surrounds it equally in every direction, so the pulls cancel exactly and \( g = 0 \). Weight is greatest at the poles, where the radius is smallest and there is no rotational effect.
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All acids are ____________
Answer: C
All acids are corrosive when strong - a concentrated strong acid attacks metal, stone and living tissue.
Dilute or weak acids are irritant rather than corrosive; citric and acetic acids are safely eaten. Corrosiveness depends on both the strength of the acid and its concentration.
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Decibel is the unit of:
Answer: C
The decibel measures the intensity, or loudness, of sound.
It is a logarithmic unit: every 10 dB is a tenfold increase in intensity, so 80 dB carries a hundred times the energy of 60 dB. Ordinary conversation is about 60 dB and a jet engine at close range about 140 dB.
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What is needed for rusting to occur?
Answer: A
Rusting needs both water and oxygen. Neither alone will do it: iron kept in dry air or in boiled, air-free water does not rust.
The product is hydrated iron(III) oxide, Fe2O3·nH2O. Dissolved salt or acid speeds the process by making the water a better electrolyte.
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