Anodising is a process of forming a thick oxide layer on which of the following?
- A.Silver
- B.Aluminium
- C.Gold
- D.Copper
Correct answer
Explanation
The correct answer is B, Aluminium. Aluminium naturally forms a thin layer of aluminium oxide when it is exposed to air, and this layer protects it from further corrosion. In anodising, the layer is made thicker on purpose. A clean aluminium article is made the anode, the positive electrode, in an electrolytic bath of dilute sulphuric acid, and the oxygen gas released at the anode reacts with the metal to build a thick oxide coat. This coat resists corrosion and scratches and can easily be dyed in attractive colours, which is why anodised aluminium is used for pressure cookers, window frames and many household articles. Option A is wrong because silver does not form a protective oxide coat; it turns black by forming silver sulphide. Option C is wrong because gold hardly reacts with air at all, so it needs no such coating. Option D is wrong because copper, in moist air, gets a green coat of basic copper carbonate, not an anodised oxide layer. Exam tip: anodising means a thick oxide layer on aluminium; galvanising means a coat of zinc on iron.
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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