Which one of the following statements is NOT correct?
- A.Water of crystallization is the fixed number of water molecules present in one formula unit of a salt
- B.The molecular formula of Plaster of Paris is CaSO4·2H2O
- C.Washing soda is used for removing the permanent hardness of water
- D.The atmosphere of Venus is made up of thick white and yellow clouds of sulphuric acid
Correct answer
Explanation
The correct answer is B, The molecular formula of Plaster of Paris is CaSO4·2H2O. The statement is false because CaSO4·2H2O is gypsum; Plaster of Paris is calcium sulphate hemihydrate, CaSO4·½H2O. When gypsum is heated to about 373 K, it loses three-quarters of its water and becomes Plaster of Paris, a white powder. Mixed with water, it sets back into hard gypsum, which is why doctors use it to hold broken bones in place and artists use it for casts and statues. Option A is wrong to pick because the statement is true: water of crystallisation is the fixed number of water molecules in one formula unit of a salt, five in blue copper sulphate. Option C is wrong to pick because the statement is true: washing soda, sodium carbonate, removes permanent hardness by precipitating calcium and magnesium ions as insoluble carbonates. Option D is wrong to pick because the statement is true: Venus is covered by thick white and yellowish clouds of sulphuric acid above a carbon dioxide atmosphere. Exam tip: gypsum = CaSO4·2H2O; Plaster of Paris = CaSO4·½H2O; washing soda = Na2CO3·10H2O.
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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