AIDS is caused by:
Answer: D
AIDS is caused by a virus - the human immunodeficiency virus, HIV.
It is a retrovirus that infects and destroys the CD4 T-lymphocytes, so the immune system gradually fails and the patient succumbs to infections a healthy person would resist.
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Wood is the main raw material for the manufacture of
Answer: B
Paper is made chiefly from wood. The wood is pulped - mechanically or with chemicals that dissolve the lignin - to free the cellulose fibres, which are then matted, pressed and dried into sheets.
Softwoods such as pine give long fibres and strength; hardwoods give shorter fibres and a smoother surface.
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Nautical mile is a unit of distance used in:
Answer: A
The nautical mile is used in navigation at sea and in the air. It equals 1,852 m, defined as one minute of arc of latitude along a meridian.
That definition is what makes it useful: a degree of latitude is 60 nautical miles, so distance can be read straight off a chart's latitude scale.
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According to Avogadro's Hypothesis, the smallest particle of an element or a compound, that can exist independently, is called:
Answer: A
Under Avogadro's hypothesis, the smallest particle of an element or compound that can exist independently is the molecule.
An atom of most elements cannot exist alone - oxygen occurs as O2, nitrogen as N2. Cations and anions are charged particles and are always found paired with an opposite charge.
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Mesons are found in
Answer: D
Mesons are found in cosmic rays.
They are produced when high-energy cosmic-ray protons strike nuclei in the upper atmosphere. The pi-meson was first identified in cosmic-ray tracks in photographic emulsion in 1947, and the muons that reach the ground come from their decay.
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Who suggested that most of the mass of the atom is located in the nucleus?
Answer: C
Ernest Rutherford concluded in 1911 that almost all an atom's mass is concentrated in a tiny nucleus.
In his gold-foil experiment most alpha particles passed straight through, but a very few bounced back - which, as he put it, was as surprising as a shell rebounding from tissue paper. Only a dense central charge could explain it.
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In vulcanisation, natural rubber is heated with
Answer: C
In vulcanisation, natural rubber is heated with sulphur.
The sulphur forms cross-links between the rubber chains, so they can no longer slide past one another. The product is harder, stronger, elastic over a wide temperature range and no longer sticky. Charles Goodyear discovered the process in 1839.
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Kilowatt is a unit to measure:
Answer: B
The kilowatt measures power - the rate of doing work, one thousand joules per second.
Energy is measured in joules, or in the kilowatt-hour of the electricity bill, which is power multiplied by time.
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Soap is a mixture of sodium or potassium salts of
Answer: B
Soap is a mixture of sodium or potassium salts of monocarboxylic acids - the long-chain fatty acids such as stearic, palmitic and oleic acid, each with a single -COOH group.
Their salts have one ionic head on a long hydrocarbon tail, which is exactly the structure needed to lift grease into water.
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Atoms of an element differ from those of all other elements in
Answer: A
Atoms of one element differ from all others in their atomic number and electronic configuration.
The atomic number - the number of protons - is what defines an element, and it fixes the number of electrons and so the configuration and the chemistry. The number of neutrons varies between isotopes of the same element, so it cannot be the distinguishing feature.
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