Question

rank the elements or compounds in the table below in decreasing order of their boiling points. that is, choose 1 next to the substance with the highest boiling point, choose 2 next to the substance with the next highest boiling point, and so on.

	a	b	c	d
	co	al₂o₃	<lewis - structure - of - a - compound>	o₂
	select	select	select	select

Explanation:

Step1: Identify substance types

$Al_2O_3$ is an ionic compound, $CO$ is a covalent - molecular compound, the Lewis - structure substance is a covalent - molecular compound (ethanol, $C_2H_5OH$), and $O_2$ is a non - polar covalent molecule.

Step2: Recall boiling - point trends

Ionic compounds have high boiling points due to strong ionic bonds. Among covalent - molecular compounds, polar molecules have higher boiling points than non - polar molecules due to dipole - dipole forces, and hydrogen - bonding molecules have even higher boiling points. $Al_2O_3$ has the highest boiling point among them. Ethanol ($C_2H_5OH$) has hydrogen bonding, so it has a higher boiling point than $CO$ (a polar molecule with only dipole - dipole forces) and $O_2$ (a non - polar molecule with only London dispersion forces). $CO$ has a higher boiling point than $O_2$ because it is polar.

Step3: Rank the substances

The ranking from highest to lowest boiling point is $Al_2O_3$ (highest, so rank 1), $C_2H_5OH$ (rank 2), $CO$ (rank 3), $O_2$ (lowest, rank 4).

Answer:

1. $Al_2O_3$
2. Substance with Lewis structure (ethanol)
3. $CO$
4. $O_2$