Which of the following represents the chemical formula for sulphur hexafluoride?
- A.S2F6
- B.SF6
- C.SF2
- D.S6F
Correct answer
Explanation
The correct answer is B, SF6. The name itself gives the formula: 'hexa' means six, so sulphur hexafluoride has one sulphur atom joined to six fluorine atoms, SF6. The molecule is octahedral in shape, with the six fluorine atoms arranged symmetrically around the sulphur. SF6 is a colourless, odourless, non-flammable and very unreactive gas, about five times heavier than air. Because it does not conduct electricity, it is used as an insulating gas inside high-voltage circuit breakers and switchgear. It is also one of the strongest greenhouse gases known, with a global warming potential thousands of times that of carbon dioxide, and it is listed under the Kyoto Protocol. A is wrong because S2F6 would need two sulphur atoms, which the name does not say. C is wrong because SF2 is sulphur difluoride, with only two fluorine atoms. D is wrong because S6F reverses the numbers and is not a real compound. Exam tip: mono 1, di 2, tri 3, tetra 4, penta 5, hexa 6; SF6 = one sulphur, six fluorine, used in electrical switchgear.
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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