The gases used in different types of welding would include
Answer: D
Welding uses oxygen and acetylene. Burning acetylene in pure oxygen gives the hottest common flame, about 3,300°C, which is above the melting point of steel.
Other processes use argon or carbon dioxide, but only as a shielding gas to keep air away from the weld, not as fuel.
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Of the following, which element is common to all acids
Answer: A
Hydrogen is the element common to all acids. An acid is defined as a substance that releases hydrogen ions (H+) in water.
Hydrochloric acid gives HCl → H+ + Cl−, sulphuric acid gives two hydrogen ions, and it is the concentration of those ions that the pH scale measures.
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Chemical formula for water is
Answer: B
Water is H2O - two hydrogen atoms bonded to one oxygen.
The molecule is bent at about 104.5°, which makes it polar, and that polarity accounts for water's high boiling point, its power as a solvent and the fact that ice floats.
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What is the chemical formula of common salt ?
Answer: C
Correct answer: NaCl
Common salt is sodium chloride, NaCl. NaOH is caustic soda, KCl is potassium chloride and CaCO3 is calcium carbonate, the chief constituent of limestone.
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In an atomic nucleus, neutrons and protons are held together by:
Answer: B
Protons and neutrons are held together in the nucleus by the strong nuclear force, carried by exchange particles - mesons in the older description, gluons in the modern one.
It is about a hundred times stronger than the electrostatic repulsion between protons, but acts only over about 10−15 m, which is why very large nuclei become unstable.
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The gas usually filled in the electric bulb is
Answer: A
Electric bulbs are filled with nitrogen, usually mixed with argon.
The inert filling stops the tungsten filament from burning up and, by being at some pressure, slows the evaporation of tungsten so the filament lasts longer and the glass blackens less. Both gases are cheap and completely unreactive at the filament's temperature.
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Electric bulb filament is made of
Answer: D
The filament of an electric bulb is tungsten.
It has the highest melting point of any metal, 3,422°C, so it can be run white-hot without melting; its high resistivity makes it glow at a modest current; and it is ductile enough to be drawn into a fine wire and coiled.
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The hardest material available on earth is
Answer: B
Diamond is an allotrope of carbon. Every atom is bonded to four others in a rigid tetrahedral network, which is what makes it the hardest natural substance.
Graphite, charcoal and the fullerenes are the other allotropes; they differ only in how the same atoms are arranged.
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In a laser (say neon laser) all the atoms emit the light waves of
Answer: D
In a laser all the atoms emit light of the same frequency, amplitude and phase.
This is what stimulated emission means: a passing photon triggers an excited atom to emit a photon identical to it in every respect. The result is a beam that is monochromatic, coherent and almost perfectly parallel.
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Lime water contains -
Answer: C
Lime water is a solution of calcium hydroxide, Ca(OH)2.
It is the standard test for carbon dioxide: the gas turns it milky by forming insoluble calcium carbonate, and further gas redissolves the precipitate as the soluble bicarbonate.
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