Which one among the following is an example of oxidation reaction ?
- A.Freezing of water
- B.Dissolving sugar in water
- C.Rusting of iron
- D.Boiling of petrol
Correct answer
Explanation
The correct answer is C, Rusting of iron. In rusting, iron combines with oxygen in the presence of water to form hydrated iron oxide, and the addition of oxygen is oxidation. Rust is mainly hydrated iron(III) oxide, Fe2O3·xH2O, a flaky reddish-brown substance that keeps peeling away and exposing fresh metal, so iron objects slowly wear out. Rusting needs both air and moisture; salty water speeds it up. It is prevented by painting, oiling or greasing, galvanising with a coat of zinc, chrome plating and making alloys such as stainless steel. Rusting is a chemical change because a new substance with different properties forms and the change cannot be undone easily. Option A is wrong because freezing of water is a physical change of state, with no new substance formed. Option B is wrong because dissolving sugar in water is a physical change; the sugar can be recovered by evaporating the water. Option D is wrong because boiling petrol only turns liquid into vapour; burning it would be oxidation. Exam tip: rusting and combustion are oxidation; freezing, boiling and dissolving are physical changes.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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