Chemistry GK Questions Quiz-34

Chemistry GK Questions Quiz-34

Chemistry Multiple Choice Questions (MCQs) Quiz for State and UPSC Civil Services Examinations. Objective Questions on Chemistry for competitive examinations.

    661. The open "Sigrees" or coal stoves often require fanning to sustain burning because of

    (1) tendency of carbon dioxide to form a layer along with dust smoke
    (2) lack of oxygen in the surroundings of sigrees
    (3) accumulation of smoke and dust over the sigrees
    (4) interrupted release of moisture from the material
    Answer:
    661. (1) Burning coal requires oxygen to chemically react. The availability of oxygen is limited in the furnace by several factors such as the friction of the air against the coal. Blowing provides more oxygen to the flame and raises the temperature of the flame. Besides, it helps to prevent carbon dioxide from forming layer along with dust smoke so as to keep the supply of oxygen intact.

    662. Browning of paper in old books is caused by

    (1) frequent use
    (2) lack of aeration
    (3) collection of dust
    (4) oxidation of cellulose
    Answer:
    662. (4) Foxing is a term describing the age-related spots and browning seen on vintage paper documents such as books, postage stamps, certificates, and so forth. It results from localized accelerated oxidation of cellulose or the effect on certain papers of the oxidation of iron, copper, etc.

    663. Aquaregia is a mixture of the following in the ratio 1 : 3 by volume

    (1) conc. HNO3 and conc. HCl
    (2) conc. HNO3 and conc.H2SO4
    (3) dil. HCl and dil. HNO3
    (4) conc. HCl and conc. HNO3
    Answer:
    663. (3) Aqua regia or nitro-hydrochloric acid is a highly corrosive mixture of acids which is formed by freshly mixing concentrated Nitric acid (HNO3) and Hydrochloric acid (HCl), optimally in a volume ratio of 1:3. It is used in dissolving gold.

    664. In deep-sea diving, divers use a mixture of gases consisting of oxygen and

    (1) hydrogen 
    (2) nitrogen
    (3) argon 
    (4) helium
    Answer:
    664. (2) Air is not the "ideal" breathing mixture for diving as with a concentration of approximately 79 percent nitrogen, compressed air poses two potential problems for all divers: susceptibility to nitrogen narcosis and at deeper depths; and decompression sickness. So divers use Nitrox, a gaseous mixture of nitrogen and oxygen. It is also known as ‘Enriched Air.’

    665. ‘Atomic theory’ of matter was given by

    (1) Avogadro 
    (2) Dalton
    (3) Newton 
    (4) Pascal
    Answer:
    665. (2) Democritus first suggested the existence of the atom, but John Dalton (1766-1844) is credited with the Atomic Theory of Matter. According to Dalton, all matter is made of atoms; atoms are indivisible and indestructible; all atoms of a given element are identical in mass and properties; and compounds are formed by a combination of two or more different kinds of atoms.

    666. Combustion of a candle is a/an

    (1) photochemical reaction
    (2) physical change
    (3) endothermic reaction
    (4) exothermic reaction
    Answer:
    666. (4) In theory, a candle is made of a solid hydrocarbon called paraffin. When the solid burns, the hydrocarbon reacts with oxygen to form carbon dioxide and water. The reaction is exothermic, meaning it releases heat to the atmosphere along with the other products.

    667. Which among the following is a covalent compound ?

    (1) Calcium chloride
    (2) Magnesium fluoride
    (3) Sodium chloride
    (4) Carbon tetrachloride
    Answer:
    667. (4) Ionic compounds are made up of a metal and nonmetal, and covalent compounds are made up of two nonmetals. In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a central carbon atom by single covalent bonds: CH4 + 4Cl2 ? CCl4 + 4HCl

    668. The highest volume of gases in lower atmosphere is comprised of

    (1) Hydrogen
    (2) Carbon dioxide
    (3) Oxygen
    (4) Nitrogen
    Answer:
    668. (4) There are a number of atmospheric gases which make up air. In the lower atmosphere or troposphere, the main gases are nitrogen and oxygen, which make up 78% and 21% of the volume of air respectively. The remaining 1% of the atmospheric gases is made up of trace gases.

    669. The percentage of carbon in cast iron is :

    (1) 0.01 to 0.25
    (2) 0.5 to 1.5
    (3) 6 to 8
    (4) 3 to 5
    Answer:
    669. (4) Cast Iron is a hard, brittle, nonmalleable ironcarbon alloy, cast into shape. It contains 2 to 4.5
    percent carbon, 0.5 to 3 percent silicon, and lesser amounts of sulfur, manganese, and phosphorus.

    670. The compound that has the least value for octane number is :

    (1) 2-methyl heptane
    (2) Iso-octane
    (3) 2,2-dimethyl hexane
    (4) n-heptane
    Answer:
    670. (4) Octane rating or octane number is a standard measure of the performance of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand. Isooctane (upper) has an octane rating of 100 whereas n-heptane has an octane rating of 0.

    671. The pair of compounds used as anaesthetic in medicines :

    (1) Ether, Ammonia
    (2) Nitrous oxide, Chloroform
    (3) Chloroform, Nitrogen dioxide
    (4) Nitrogen dioxide, ether
    Answer:
    671. (2) Nitrous oxide is one of the more well-known anesthetic gases, and has been in use for around 200 years. Unlike some other anesthetics, this compound can be used both for inducing unconsciousness and pain control. Chloroform is more potent and more toxic than ether. Its use as an anaesthetic decreased with increased experience and knowledge of its dangers.

    672. pH scale ranges from

    (1) 0 – 7 
    (2) 8 – 14
    (3) 0 – 14 
    (4) None
    Answer:
    672. (3) The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic. The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value.

    673. Iron rusts quickly in

    (1) Rain water
    (2) Sea water
    (3) Distilled water
    (4) River water
    Answer:
    673. (2) Water is the enabler of fast oxidation of iron. So freshwater will also cause rust. However, salt water (sea water) is a very good conductor (lots of dissociated ions) and so there are a number of electrolysis reactions that tremendously accelerate corrosion in salt water. This effect can be reversed by using a metal (like zinc) which causes the current to be reversed and in effect the zinc corrodes rapidly, protecting the iron.

    674. Aerated water contains

    (1) SO2 
    (2) NO2
    (3) H2 
    (4) CO2
    Answer:
    674. (4) Aerated water is, correctly speaking, water to which air is added. So aerated water is any water artificially impregnated with a large amount of gas (as carbon dioxide). The term is, however, frequently applied to carbonated water.

    675. Magnetite is

    (1) Fe2O3 
    (2) Fe3O4
    (3) FeCO3 
    (4) 2Fe2O3. 3H2O
    Answer:
    675. (2) Magnetite is a mineral, one of the two common naturally occurring iron oxides (chemical formula Fe3O4). It is the most magnetic of all the naturally occurring minerals on Earth. The chemical IUPAC name of magnetite is iron oxide and the common chemical name is ferrous-ferric oxide.

    676. Iron is prevented from rusting by coating with zinc. This process is called as

    (1) Galvanisation
    (2) Corrosion
    (3) Sublimation
    (4) Reduction
    Answer:
    676. (1) Galvanization is the process of applying a protective zinc coating to steel or iron, in order to prevent rusting. The term is derived from the name of Italian scientist Luigi Galvani. Although galvanization can be done with electrochemical and electro-deposition processes, the most common method in current use is hot-dip galvanization, in which steel parts are submerged in a bath of molten zinc.

    677. Which of the following is the maximum number of electrons that can be present in M-shell?

    (1) 2 
    (2) 8
    (3) 18 
    (4) 32
    Answer:
    677. (3) The maximum number of electrons that can occupy a specific energy level can be found using the following formula: Electron Capacity = 2n2. The variable n represents the Principal Quantum Number, the number of the energy level in question. Since the M-shell belongs to 3rd energy level, its electron capacity = 2 × 32 = 18

    678. In an oxygen molecule, two atoms are united by

    (1) one bond 
    (2) two bonds
    (3) three bonds 
    (4) four bonds
    Answer:
    678. (2) Two oxygen atoms can both achieve stable structures by sharing two pairs of electrons as in the diagram. Two electrons of each of the atom in the oxygen molecule make the double bond with each other. The double bond is shown conventionally by two lines joining the atoms. Each line represents one pair of shared electrons.

    679. The inert gas which is substituted for nitrogen in the air used by deep sea divers for breathing is

    (1) Neon 
    (2) Krypton
    (3) Argon 
    (4) Helium
    Answer:
    679. (4) Helium is used by deep sea divers because it reduces the narcosis of nitrogen and it remains below the oxygen toxicity limits. In fact, they use tri mix of Oxygen, helium and a little bit of nitrogen.

    680. How many neutrons are there in 92U238 atom ?

    (1) 92 
    (2) 238
    (3) 146 
    (4) 330
    Answer:
    680. (3) The atomic mass (A) of Uranium (92U238) = 238; the number of protons (p) = 92 = number of electrons (e). Since atomic mass (A) = p + n (number of neutrons), A = 238 = 92 + n So, n = 238 -92 = 146


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