Which of the following substances are present on the rubbing surface of a matchbox?
- A.Glass powder and red phosphorus
- B.White phosphorus and glass powder
- C.Red phosphorus and magnesium
- D.Potassium and white phosphorus
Correct answer
Explanation
The correct answer is A, Glass powder and red phosphorus. The rough strip of a safety matchbox is coated with powdered glass and a little red phosphorus, while the head of the matchstick carries antimony trisulphide and potassium chlorate. When the match is struck, friction turns some red phosphorus into white phosphorus. This reacts at once with the potassium chlorate in the head and produces enough heat to set the antimony trisulphide burning. Keeping the phosphorus on the box and the other chemicals on the stick is what makes the match safe. NCERT's Class 8 science book adds that early matches used white phosphorus, which proved dangerous for the workers who made them and for users. B is wrong because white phosphorus is not used on the rubbing surface of a safety match. C is wrong because magnesium is not part of the striking strip. D is wrong because neither potassium nor white phosphorus is found on the strip. Exam tip: box strip, red phosphorus plus glass powder; match head, antimony trisulphide plus potassium chlorate.
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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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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