1. An example of physical change –
(a) Blackening of silverware
(b) Burning of Candle
(c) Making of curd from milk
(d) Dissolving of sugar in water
[38th B.P.S.C. (Pre) 1992]
Ans. (d) Dissolving of sugar in water
- A physical change affects how something looks, but not what it is made of.
- This is different from a chemical change, which involves changing what the substance is made of.
- Usually, physical changes happen when physical forces are used.
- For example, when you dissolve sugar in water you can get the sugar back by evaporating the water.
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2. The change of water into the vapour is called –
(a) Natural
(b) Physical
(c) Chemical
(d) Biological
[U.P.P.C.S. (Pre) 1992]
Ans. (b) Physical
- Water turning into steam is a physical change.
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3. Which of the following is an example of chemical change–
(a) Dispersion of white light into the light of 7 colours when passed through a prism
(b) Softening of vegetables when cooked
(c) Wet soil lump, when dried, gets fragile
(d) Dissolving of salt in water
[R.A.S./R.T.S. (Pre) 2003]
Ans. (b) Softening of vegetables when cooked
- A chemical change is when something is changed in a way that its characteristics are different than before.
- This means that its molecules have changed and it will be in a different state.
- An example of this is cooking vegetables, which causes permanent changes in the vegetables’ composition.
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4. Which of the following is/are the example/examples of chemical change?
1. Crystallization of sodium chloride
2. Melting of ice
3. Souring of milk
Select the correct answer using the code given below.
(a) 1 and 2 only
(b) 3 only
(c) 1, 2 and 3
(d) None
[I.A.S. (Pre) 2014]
Ans. (b) 3 only
- A chemical change is when something new is made and the original materials become something different.
- The new material will have a different chemical make-up than what it started as.
- Examples of chemical change could be rusting of iron or a metal reacting with acid.
- Physical changes, like salt crystals forming or ice melting, do not create something new.
- However, souring of milk is an example of a chemical change.
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5. Assertion (A): A chemical reaction becomes faster at a higher temperature.
Reason (R): At higher temperatures, molecular motion becomes more rapid.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not a correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
[I.A.S. (Pre) 2001]
Ans. (a) Both (A) and (R) are true and (R) is the correct explanation of (A).
- When temperatures increase, molecules move faster and have more energy.
- This makes chemical reactions happen more quickly.
- The speed of a reaction is affected by how concentrated the molecules are, the temperature and physical state, and the type of molecules.
- Generally, the higher the temperature, the faster the reaction.
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6. What form of energy is produced in the decomposition of water?
(a) Light
(b) Heat
(c) Sound
(d) Acid
[M.P.P.C.S. (Pre) 1997]
Ans. (b) Heat
- Hydrolysis is a chemical process in which a salt that is dissolved in water reacts with a water molecule, creating either an acidic or basic solution.
- Heat is released as a result of this reaction.
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7. Pasteurization is a process by which –
(a) Milk is preserved at a very low temperature for 24 hours
(b) Milk is heated for 8 hours
(c) First milk is heated up for a longer time and then cooled suddenly within the specified time
(d) None of these
[38th B.P.S.C. (Pre) 1992]
Ans. (c)First milk is heated up for a longer time and then cooled suddenly within the specified time
- Pasteurization was first invented by French scientist Louis Pasteur in the nineteenth century.
- He found that if you heat beer or wine, it will kill most of the bacteria that make it spoil and go bad.
- This process of heating and cooling milk quickly is called pasteurization and it helps to keep the milk fresh for longer.
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8. Pasteurization is related to :
(a) Sterilization of milk
(b) Dehydration of milk
(c) Fermentation of milk
(d) Distillation of milk
[M.P. PCS (Pre) 2016]
Ans. (a) Sterilization of milk
- Pasteurization is a way to get rid of germs (mainly bacteria) in food and drinks, like milk, and make it last longer and be safer.
- It works by heating the milk at a specific temperature for a certain amount of time.
- The temperature is usually either 630 C for 30 minutes, or 720 C for 15 seconds.
- This process was invented by the French scientist Louis Pasteur, so it was named after him.
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9. Which of the following is NOT correctly matched?
(a) Desalination Seawater
(b) Reverse osmosis Potable water
(c) Denaturation Proteins
(d) Pasteurization Tea
[U.P.P.C.S. (Pre) 2019]
Ans. (d) Pasteurization Tea
- Pasteurization was invented by Louis Pasteur in 1864 and is used to make drinks like milk, wine and fruit juices safer to drink and last longer.
- However, pasteurization is not used for tea.
- Other food items can be paired with pasteurization.
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10. Because of impurities the boiling point of a liquid –
(a) Increases
(b) Decreases
(c) Remains constant
(d) They are not related
[M.P.P.C.S. (Pre) 2004]
Ans. (a) Increases
- The boiling point of a liquid is the temperature at which the pressure of the gas above it is the same as the pressure of its vapour.
- When any liquid is mixed with impurities, the boiling point gets higher.
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11. Give a thought to these statements :
Statement (A): Temperature below 0o C is achieved by the mixture of salt and ice.
Reason (R): Salt increases the freezing point of ice. In the context of the above statements which one of the following is correct:
(a) (A) and (R) are both correct, and (R) is the correct explanation of (A).
(b) (A) and (R) are both correct, but (R) is not the correct explanation of (A).
(c) (A) is correct but (R) is wrong.
(d) (A) is wrong but (R) is correct.
[U.P. Lower Sub. (Pre) 1998, I.A.S. (Pre) 1993]
Ans. (c) (A) is correct but (R) is wrong
- When something dirty is added to a liquid, it changes the temperature at which it boils and it gets higher.
- When salt (like NaCl or KNO3) is added to ice, it makes the temperature go down below 0o C.
- This mixture is called a freezing mixture.
- So, Statement A is correct, but Reason R is not.
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12. Milk is an example of :
(a) A gel
(b) A foam
(c) An emulsion
(d) A suspension
[42nd B.P.S.C. (Pre) 1997, U.P.P.C.S. (Pre) 1996]
Ans. (c) An emulsion
- An emulsion is a mixture of two or more liquids that don’t usually mix together.
- Milk is an example of an emulsion, since it is a mixture of oil and water.
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13. Which of these is not a colloid :
(a) Milk
(b) Blood
(c) Icecream
(d) Honey
[U.P.P.C.S. (Pre) 2002]
Ans. (d) Honey
- Honey is different from milk, blood, and ice cream because it is not a colloid.
- At room temperature, honey is a supercooled liquid, containing solid pieces of glucose in a solution of fructose and other ingredients.
- Milk, blood, and ice cream, however, are all colloids.
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14. Which type of colloidal system is expressed in the fog :
(a) Liquid in a gas
(b) Gas in a liquid
(c) Solid in a gas
(d) Liquid in Liquid
[I.A.S. (Pre) 1993]
Ans. (a) Liquid in a gas
- When the air is cold during winter, the water vapor in the air turns into tiny droplets that form fog.
- This happens when the temperature gets close to the dew point and the water vapor sticks to small dust particles in the air and remains in the air because they are so light.
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15. If an unsaturated sugar solution is prepared by mixing 100 grams of sugar with half a litre of water, which of the following physical quantities will not change?
(a) Mass
(b) Density
(c) Concentration
(d) Volume
[U.P.P.C.S. (Pre) 2017]
Ans. (d) Volume
- If you mix 100 grams of sugar with 500 milliliters of water, the amount of liquid stays the same.
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16. After cutting the cucumber if salt is added, then water comes out due to :
(a) Active transport
(b) Passive transport
(c) Osmosis
(d) Difusion
[U.P. P.C.S. (Pre) 2021]
Ans. (c) Osmosis
- Osmosis is when water molecules move from an area with less concentration to an area with more concentration through a special membrane.
- When salt is added to cucumber or cut onion pieces, their environment becomes more concentrated than the cells inside them.
- This causes the water molecules in those cells to move out through the cell membrane (which is porous).
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17. Consider the following statements :
1. During the process of osmosis, the solvent travels from the concentrated solution to the dilute solution.
2. In reverse osmosis, external pressure is applied to the dilute solution.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
[I.A.S. (Pre) 2005]
Ans. (d) Neither 1 nor 2
- Osmosis is when a solvent moves through a special filter to balance out the concentration of a substance.
- For reverse osmosis, pressure is used to push the solvent the opposite way, from a concentrated solution to a weaker one.
- This process is often used to purify a solution and remove any impurities.
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18. Which one of the following processes is NOT useful for the purification of solid impurities?
(a) Distillation
(b) Sublimation
(c) Crystallization
(d) All of the above
[U.P. R.O./A.R.O. (Pre) (Re. Exam) 2016]
Ans. (a) Distillation
- Distillation is the process of cleaning a liquid by heating and cooling it.
- Usually, distillation is used to remove impurities from liquids, and sublimation and crystallization are used to remove impurities from solids.
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19. The technique of chromatography is used to –
(a) Identify colour substances
(b) Determine the structure of substances
(c) Dry distillation of colouring substances
(d) Separate the substances from a mixture
[42nd B.P.S.C. (Pre) 1997]
Ans. (d) Separate the substances from a mixture
- Chromatography is a method of separating different parts of a liquid mixture.
- It works by having the components pass through a mobile and stationary phase.
- Depending on the goal, it can be used for either purifying or analyzing the mixture.
- Preparative chromatography is used to separate the components of the mixture for further use.
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20. The process of solid camphor into camphor vapour is called:
(a) Vaporization
(b) Freezing
(c) Melting
(d) Sublimation
[44th B.P.S.C. (Pre) 2000]
Ans. (d) Sublimation
- When solid camphor is heated, it directly transforms into camphor vapour.
- This is known as sublimation.
- It is a process where a substance turns directly into a vapour when heated, and then becomes solid again when cooled.
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21. A sample of any of the following substances disappears after some time when exposed to air like camphor, naphthalene or dry ice. This phenomenon is called :
(a) Sublimation
(b) Evaporation
(c) Diffusion
(d) Radiation
[U.P.P.C.S. (Pre) 2019]
Ans. (a) Sublimation
- Sublimation is when a solid material goes directly into a gas, without becoming a liquid first.
- Examples of this are camphor, naphthalene, and dry ice (frozen carbon dioxide).
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22. The conversion of a solid directly into gas is called as :
(a) Sublimation
(b) Condensation
(c) Evaporation
(d) Boiling
(e) None of the above/More than one of the above
[63rd B.P.S.C. (Pre) 2017]
Ans. (a) Sublimation
- Sublimation is when a solid material turns straight into a gas without becoming a liquid first.
- Examples of this are camphor, naphthalene, and dry ice (frozen carbon dioxide).
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23. A mixture of sand and naphthalene can be separated by :
(a) sublimation
(b) distillation
(c) chromatography
(d) fractional distillation
(d) None of the above / More than one of the above
[66th B.P.S.C. (Pre) 2020]
Ans. (a) sublimation
- When heated, naphthalene changes directly from a solid to a gas.
- This process is called sublimation.
- This means that a mixture of sand and naphthalene can be separated by heating it.
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24. Match List-I (oxidation number) with List-II (the element) and select the correct answer using the codes given below the lists :
List-I List-II
A. 2 1. Oxidation number of Mn in MnO2
B. 3 2. Oxidation number of S in H2 SO4
C. 4 3. Oxidation number of Ca in CaO
D. 6 4. Oxidation number of Al in NaAlH4
Code :
A B C D
(a) 3 4 1 2
(b) 4 3 1 2
(c) 3 4 2 1
(d) 4 3 2 1
[I.A.S. (Pre) 2002]
Ans. (a) 3 4 1 2
- The oxidation number of any compound is always zero.
- This means that sum of the oxidation number of all the elements present in the compound is zero.
- By this rule, we can now find the oxidation number in given options here –
- (1) Suppose, the oxidation number of Mn in MnO2 is x.
- MnO2 contains two oxygen ions, each with an oxidation number (–2).
- x + 2 × (–2) = 0 x – 4 = 0
- x = 4
- (2) Suppose, the oxidation number of S in H2 SO4 is x.
- H2 SO4 contains two hydrogen ion, each with an oxidation number (+1) and oxidation number of oxygen
- (–2). 2 (+1) + x + 4 (–2) = 0
- 2 + x – 8 = 0
- x = 6
- (3) The oxidation number of Ca in CaO when oxygen has oxidation number (–2)
- (4) Suppose, the oxidation number of Al in NaAlH4 is x.
- NaAlH4 contains one Na which has oxidation number (+1) and four H which has oxidation number (–1).
- (+1) + x + 4 (–1) = 0
- 1 + x – 4 = 0
- x = 3
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25. An example of corrosion is –
(a) Black coating on Silver
(b) Green coating on Copper
(c) Brown coating on Iron
(d) Above three
(e) None of the above
[Chhattisgarh P.C.S. (Pre) 2016]
Ans. (d) Above three
- Metals breaking down slowly due to air or other chemicals is called corrosion.
- Examples of this include rusting on iron, a green coating on copper, and a black coating on silver.
- Chromatography is a way of sorting out the different parts of a liquid mixture.
- It can be used to prepare or analyze the mixture and is a form of cleaning up the components.
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