Explanation:

The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a stable configuration of 8 valence electrons. This rule is applicable to most elements in the periodic table, especially those from the second period onwards.

However, there are exceptions to the octet rule, particularly for certain elements in the third period and beyond, such as phosphorus, sulfur, and elements in the d and f block. These elements can accommodate more than 8 valence electrons due to the presence of empty d or f orbitals.

In the given options, the molecule NO (nitric oxide) does not follow the octet rule.

Explanation of NO:

- Nitric oxide (NO) consists of a nitrogen atom (N) bonded to an oxygen atom (O).
- Nitrogen has 5 valence electrons, while oxygen has 6 valence electrons.
- In order to achieve an octet, nitrogen would need to gain 3 electrons or share 3 pairs of electrons.
- However, in NO, nitrogen forms a triple bond with oxygen, sharing 3 pairs of electrons. This results in a total of 8 electrons around the nitrogen atom, violating the octet rule.
- The Lewis structure for NO is N≡O, where the triple bond represents the sharing of 3 pairs of electrons between nitrogen and oxygen.

Exceptions to the octet rule:

- Elements in the third period and beyond can accommodate more than 8 electrons due to the presence of empty d or f orbitals.
- These elements can form expanded octets, where they have more than 8 valence electrons.
- Phosphorus pentachloride (PCl5) and sulfur hexafluoride (SF6) are examples of molecules that follow the expanded octet rule.
- In PCl5, phosphorus forms 5 single bonds with chlorine, resulting in a total of 10 valence electrons around the phosphorus atom.
- In SF6, sulfur forms 6 single bonds with fluorine, resulting in a total of 12 valence electrons around the sulfur atom.

In conclusion, the molecule NO does not follow the octet rule, as nitrogen forms a triple bond with oxygen, resulting in 8 valence electrons around the nitrogen atom.