Introduction:

The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a stable electron configuration with a full outer shell of eight electrons. This rule generally applies to main group elements in period 2 and beyond. However, there are some exceptions to the octet rule, where atoms can have fewer or more than eight electrons in their valence shell.

Explanation:

A) CO2:
Carbon dioxide (CO2) follows the octet rule. Carbon has 4 valence electrons, while each oxygen atom has 6 valence electrons. Carbon shares two electrons with each oxygen atom, resulting in a total of 8 electrons around the carbon atom and 8 electrons around each oxygen atom.

B) PCl3:
Phosphorus trichloride (PCl3) does not follow the octet rule. Phosphorus has 5 valence electrons, and each chlorine atom has 7 valence electrons. In PCl3, phosphorus shares three electrons with each chlorine atom, resulting in a total of 10 electrons around the phosphorus atom. This exceeds the octet rule.

C) ICl:
Iodine monochloride (ICl) follows the octet rule. Iodine has 7 valence electrons, and chlorine has 7 valence electrons. Iodine shares one electron with chlorine, resulting in a total of 8 electrons around iodine and 8 electrons around chlorine.

D) ClF3:
Chlorine trifluoride (ClF3) does not follow the octet rule. Chlorine has 7 valence electrons, and each fluorine atom has 7 valence electrons. In ClF3, chlorine shares one electron with each fluorine atom, resulting in a total of 10 electrons around the chlorine atom. This exceeds the octet rule.

Conclusion:

Out of the given compounds, phosphorus trichloride (PCl3) and chlorine trifluoride (ClF3) do not follow the octet rule. These compounds have more than eight electrons around the central atom due to the presence of additional lone pairs. It is important to note that there are exceptions to the octet rule, particularly for elements in period 3 and beyond, as they can accommodate more than eight electrons in their valence shell.