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Part 066 – Chemistry Previous Year Questions

Q1. The gas that causes suffocation and death when coal or coke is burnt in a closed room is
(a) Methane
(b) Ethane
(c) Carbon monoxide
(d) Carbon di–oxide
Ans: (c) Exhaust fumes of motor cars, gases produced from coal fire in a closed room and coal gas, all contain carbon monoxide, which is the cause of their poisonous nature. When carbon monoxide is inhaled, it prevents the oxygen from combining with hemoglobin and instead combines itself with hemoglobin to form carboxyhaemoglobin, which is stable compound. This causes oxygen starvation in the body tissues and eventually causes death by suffocation.

Q2. Air is said to be saturated when :

(a) it contains maximum content of water vapour
(b) its pressure is minimum
(c) its thickness is maximum
(d) it blows over the barren land
Ans: (a) When a volume of air at a given temperature holds the maximum amount of water vapour, the air is said to be saturated. Air is said to be saturated at 100 percent relative humidity when it contains the maximum amount of moisture possible at that specific temperature. When relative humidity reaches 100 percent or is saturated, moisture will condense, meaning the water vapor changes to liquid vapor.

Q3. Atoms having the same number of protons but different number of neutrons are called :

(a) Isotopes (b) Cations
(c) Higgs-boson (d) Anions
Ans: (a) Atoms that have the same number of protons but different numbers of neutrons are called isotopes. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons, so that the neutron numbers of these isotopes are 6, 7 and 8 respectively.

Q4. Soap helps in better cleaning of clothes because

(a) Soap acts like catalyst
(b) It reduces the surface tension of solution
(c) It gives strength to solution
(d) It absorbs the dirt
Ans: (b) Soaps are effective cleaners because they can dissolve and the oil and grease that holds dirt in place. They reduce the surface tension of the solution and enable it to wet things more uniformly. The surfactants in detergents improve water’s ability to wet things, spread over surfaces, and seep into dirty clothes fibers. The surfactant molecules help water to get a hold of grease, break it up, and wash it away.

Q5. The most suitable unit for expressing nuclear radius is :

(a) nanometre (b) fermi
(c) angstrom (d) micron
Ans: (c) The atomic radius is a measure of the size of an atom. It is defined as one-half the distance between the nuclei of two identical atoms that are bonded together. Angstrom is the most common unit used for measuring atomic radius. It is equivalent to 1.0 × 10- 10 meters. Under most definitions the radii of isolated neutral atoms range between 30 and 300 pm (trillionths of a metre), or between 0.3 and 3 angstroms.

Q6. Iron filings can be separated from a heterogenous mixture using the technique of :

(a) Sublimation
(b) Magnetization
(c) Sedimentation
(d) Evaporation
Ans: (b) The method of separation using magnets is used when one of the components is magnetic. So the heterogeneous mixture of iron filings and some other material (such as sulphur powder) can be separated by using magnets. Similarly, a mixture of sand and iron filings can be separated by magnet.

Q7. The most abundant element by number in the living system is :

(a) Nitrogen (b) Hydrogen
(c) Oxygen (d) Carbon
Ans: (b) In sequential order, Hydrogen, Oxygen, Carbon and Nitrogen are the most abundant elements by number in the living system. Hydrogen constitutes 49.8% of living systems, while Oxygen constitutes 24.9%; Carbon and Nitrogen account for 24.9% and 0.27% respectively. It is not surprising, therefore, that the living cell is between 60% and 90% water.

Q8. The “King of Metals” is :

(a) Gold (b) Silver
(c) Iron (d) Aluminium
Ans: (a) Gold, which is not only the most valuable of metals, but also is without its peer in freedom from alloy, is known as the king of metals. Luxurious, classy and beautiful, gold is the most classic and coveted jewelry metal of all. It is also the oldest precious metal known to man.

Q9. The strongest oxidizing agent among the following is:

(a) Chlorine (b) Iodine
(c) Fluorine (d) Oxygen
Ans: (c) An oxidizing agent is a chemical species that removes an electron from another species. Fluorine, having the largest positive value of electrode potential, is the strongest oxidizing agent. As a matter of fact, all halogens have a tendency to take up electrons and thus act as strong oxidizing agents. Among them, Fluorine (the most electronegative element) is given a value of 4.0 and is the strongest oxidizing agent which is reflected in its highly positive standard potential (Eo = +2.85 V). The oxidizing power decreases from fluorine to iodine. Fluorine is so strong an oxidizing agent that it is impossible to carry out reactions with it in aqueous solution. 2F2+H2O 4HF+O2

Q10. Organic food is supposed to be better for human consumption because :

(a) It is grown in glass house & air tight environment.
(b) It is grown without the use of chemicals & synthetic pesticides.
(c) It depends on chemicals & fertilizers.
(d) It is too expensive to buy.

Ans: (b) There are at least two good arguments for eating organic: fewer pesticides and more nutrients. In the absence of pesticides and fertilizers, plants boost their production of the phytochemicals (vitamins and antioxidants) that strengthen their resistance to bugs and weeds. A major new study has found that organic foods contain higher levels of antioxidants and less harmful chemicals than conventionally farmed produce.

Q11. The main component of liquid bleach is:

(a) Sodium chloride
(b) Sodium hypochlorite
(c) Hydrochloric acid
(d) Sodium hypochlorate
Ans: (b) Sodium hypochlorite bleaches are also called chlorine or liquid household bleach. They are the more powerful laundry bleaches; they are used to whiten and disinfect laundry, is typically either 5.25 percent (regular strength) or 6 percent sodium hypochlorite (ultra strength).

Q12. Chile saltpeter is the common name of:

(a) Sodium nitrate
(b) Potassium nitrite
(c) Potassium nitrate
(d) Sodium nitrite
Ans: (a) Sodium Nitrate (NaNO3) is also known as Chile saltpeter or Peru saltpeter (due to the large deposits found in the Atacama desert in these countries) to distinguish it from ordinary saltpeter, potassium nitrate. Also known as soda niter, it is used in the production of fertilizers, pyrotechnics and smoke bombs, glass and pottery enamels, food preservatives, and solid rocket propellant

Q13. The gas liberated in the Bhopal gas tragedy was:

(a) Pheynl isocynate
(b) Acetylene
(c) Ethylene
(d) Methyl isocynate
Ans: (d) The Bhopal gas tragedy involved the leakage of poisonous methyl isocyanate (MIC) gas and other chemicals at the Union Carbide India Limited (UCIL) pesticide plant in Bhopal, Madhya Pradesh, on the night of 2–3 December 1984. It is considered the world’s worst industrial disaster.

Q14. In a reaction of the type A+B C+D one could ensure it to be a first order reaction by :

(a) Increasing the temperature
(b) Increasing the concentration of a product
(c) Increasing the concentration of a reactant
(d) Adding a catalyst
Ans: (c) A first-order reaction is a reaction that proceeds at a rate that depends linearly on only one reactant concentration. In other words, when the reaction rate depends on the first power of concentration of a single reactant,’ it is considered to be first order. The rate of reaction is directly proportional to the concentration of reacting substance. Absorption, distribution, elimination rates are examples of such reaction. The following graph represents concentration of reactants versus time for a first-order reaction: Concentration Time

Q15. Stalactites and Stalagmites form due to the precipitation of :

(a) CaCO3 (b) CaCl2
(c) MgCl2 (d) MgCO3
Ans: (a) Stalactites and stalagmites are formed by water dripping or flowing from fractures on the ceiling of a cave. The dominant mineral in them is calcite (calcium carbonate) or CaCaO3. Their largest displays are formed in caves of limestone and dolomite. Other minerals that may be deposited include other carbonates, opal, chalcedony, limonite, and some sulfides.

Q16. Soldering of two metals is possible because of the property of :

(a) Viscosity (b) Osmosis
(c) Cohesion
(d) Surface tension
Ans: (c) Soldering is the process of joining two metals by the use of a solder alloy, and it is one of the oldest known joining techniques. It is possible because of the property of cohesion, the interaction between adjacent parts of the same body and as acting throughout the interior of substance. Soldering leads to alloy formation at the layer between two metals.

Q17. An electrochemical cell which is used as a source of direct electrical current at constant voltage under standard conditions is called a :

(a) Power transmittor
(b) Battery
(c) Uninterrupted power supply
(UPS)
(d) Generator
Ans: (b) A Galvanic cell, also known as battery, is an electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell. It is typically used as a source of electrical power. By their nature, they produce direct current. A battery is a set of galvanic cells that are connected in parallel.

Q18. The gas dissolved in water that makes it basic is :

(a) ammonia
(b) sulphur dioxide
(c) hydrogen
(d) carbon dioxide
Ans: (a) Ammonia gas that dissolves in water forms a solution of ammonium hydroxide (NH4OH). This solution (including the gas) is a strong base and will make the solution alkaline. H2O + NH3 OH– + NH4 +

Q19. The number of hydrogen bonds between guanine and cytosine in DNA is

(a) 2 (b) 3
(c) 4 (d) 1
Ans: (b) The chemistry of the nitrogenous bases is really the key to the function of DNA. It allows something called complementary base pairing. Cytosine can form three hydrogen bonds with guanine, and adenine can form two hydrogen bonds with thymine. Guanie H Cytosine H H H H N N N N N N N N    – – – 1 O 6 2 2 4 3 O

Q20. The deterioration of a metal by an electrochemical process is commonly termed as

(a) Erosion (b) Corrosion
(c) Passivation (d) Abrasion
Ans: (b) Corrosion can be defined as the deterioration of materials by chemical processes. Of these, the most important by far is electrochemical corrosion of metals, in which the oxidation process M ? M+ + e– is facilitated by the presence of a suitable electron acceptor, sometimes referred to in corrosion science as a depolarizer.

Q21. Which gas emitted by power stations causes acid rain?

(a) Carbon dioxide
(b) Sulphur dioxide
(c) Helium
(d) Nitrogen
Ans: (b) Sulfur dioxide (SO2) and nitrogen oxides (NOx) are the principal pollutants that cause acid rain. SO2 and NOx emissions released to the air react with water vapor and other chemicals to form acids that fall back to Earth. Power plants burning coal and heavy oil produce over two-thirds of the annual SO2 emission.

Q22. Heavy water is

(a) Deuterium
(b) Rain water
(c) Tritium oxide
(d) Deuterium oxide
Ans: (d) Heavy water is deuterium oxide (2H2O). It is a form of water that contains a larger than normal amount of the hydrogen isotope deuterium (2H or D, also known as heavy hydrogen), rather than the common hydrogen-1 isotope (1H or H, also called protium) that makes up most of the hydrogen in normal water.

Q23. Which of the following is the strongest base in aqueous solution ?

(a) Diethylamine
(b) Triethylamine
(c) Ammonia
(d) Ethylamine
Ans: (a) Amines are organic derivatives of ammonia, in which one, two, or all three of the hydrogens of ammonia are replaced by organic groups. All aliphatic primary amines are stronger bases than ammonia.In aqueous solution, the pKb’s (basicity) of ammonia, methyl amine, dimethylamine, and trimethyl amine are therefore, respectively, 4.74, 3.34, 3.27. and 4.19. In terms of pKb, the strongest bases have the least positive values of pKb. So in aqueous solutions, the strongest bases are: Dimethylamine > methylamine > trimethylamine.>ammonia (asked in IIT JEE Exam).

Q24. The inert gas which is substituted for nitrogen in the air used by deep sea divers for breathing, is

(a) Xenon (b) Krypton
(c) Argon (d) Helium
Ans: (d) Trimix is a breathing gas, consisting of oxygen, helium and nitrogen, and is often used in deep commercial diving. The helium is included as a substitute for some of the nitrogen, to reduce the narcotic effect of the breathing gas at depth. It helps to reduce nitrogen narcosis and to avoid the dangers of oxygen toxicity. With a mixture of three gases, it is possible to create mixes suitable for different depths or purposes by adjusting the proportions of each gas.

Q25. An acid having basicity one is

(a) Sodium dihydrogen phosphate
(b) Disodium hydrogen phosphate
(c) Sodium phosphate
(d) Phosphoric acid
Ans: (b) The basicity of an acid is the number of hydrogen ions (H+) which can be produced by the ionization of one molecule of the acid in aqueous solution. For example, the basicity of hydrochloric acid is 1 since one molecule of HCl produces one H+ ion in solution. Similarly, the basicity of Disodium phosphate (Na2HPO4) is one since it has one H+ displaceable ion.

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