The temperature at which solid melts to become a liquid at the atmospheric pressure is called its melting point. The melting point of a solid is an indication of
- A.Strength of the intermolecular forces of attraction
- B.strength of the intermolecular forces of repulsion
- C.molecular mass
- D.molecular size
Correct answer
Explanation
The correct answer is A, strength of the intermolecular forces of attraction. Melting means breaking the particles free of the forces holding them in a fixed lattice, so a higher melting point means stronger forces of attraction. Heat supplied at the melting point does not raise the temperature at all; it is used as latent heat of fusion to overcome those attractions. This is why ionic solids such as common salt melt near 800 degrees Celsius while wax, held together by weak forces, melts in the warmth of a hand. Option B is wrong because repulsive forces act only when particles are pushed very close and they do not hold a solid together. Option C is wrong because molecular mass is a poor guide, as heavy iodine melts far below lighter silica. Option D is wrong because size matters only through the strength of the forces it creates, not on its own. Exam tip: stronger intermolecular forces mean a higher melting point and a higher boiling point together.
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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