The freezing point of helium is -270°C. The freezing point of xenon is-112°C. Bo

Question

The freezing point of helium is -270°C. The freezing point of xenon is-112°C. Both of these are in the noble gas family. Which of the following statements is supported by these data? A) Helium and xenon form highly polar molecules. B) As the C) The London dispersion forces between the helium molecules are greater than the 18. molecular weight of the noble gas increases, the freezing point decreases. London dispersion between the xenon molecules. The London dispersion forces between the helium molecules are less than the London dispersion forces between the xenon molecules. None of these. D) E) 10

Explanation / Answer

The answer is option D.

The reason is that the molecules having stronger intermolecular forces have higher freezing points. When a substance is cooled, the kinetic energy of atoms reduces and they come closer to each other. If the intermolecular forces are stronger, then the particles come closer fast enough and settle down to freeze. Hence the freezing point reaches early at lesser negative value as for xenon. So xenon has stronger intermolecular forces/London dispersion forces when compared to helium. Molecules having lower intermolecular forces won't freeze until temperature is lowered further. Also, helium and xenon cannot form polar molecules as they are Noble gases. Mild polarity exists due to London dispersion forces. Hence option A is also wrong.

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