Which one of the following is the best example of desiccant ?
- A.Silica gel
- B.Polystyrene
- C.Sodium chloride
- D.Sodium carbonate
Correct answer
Explanation
The correct answer is A, Silica gel. A desiccant is a substance that absorbs moisture from its surroundings and keeps things dry, and silica gel is the most widely used one.
Silica gel is a porous, granular form of silicon dioxide (SiO₂). Its tiny pores give it a very large surface area, so it holds water vapour on its surface by adsorption. That is why small sachets of silica gel are packed with shoes, medicines, cameras and electronic goods. Other common drying agents in the laboratory are anhydrous calcium chloride, concentrated sulphuric acid and quicklime.
B is wrong: polystyrene is a plastic used in packing foam and disposable cups, and it repels water rather than absorbing it. C is wrong: common salt can pick up a little moisture when impure, but it is not used as a drying agent. D is wrong: sodium carbonate is washing soda, used for softening hard water and in making glass.
Exam tip: Silica gel = SiO₂, a desiccant that works by adsorption; the blue indicator kind turns pink when it is saturated with water.
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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