The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a full outer shell of eight electrons. However, there are several exceptions to this rule.

• Incomplete Octet: Some elements are stable with fewer than eight electrons in their valence shell.
• Expanded Octet: Elements in period 3 and beyond can accommodate more than eight electrons in their valence shell due to the availability of d-orbitals.
• Odd-Electron Molecules: Molecules with an odd number of valence electrons cannot satisfy the octet rule for all atoms.

Let's analyze each option:

A) AlCl${}_3$:

• Aluminum (Al) is in Group 13 and has 3 valence electrons. In AlCl${}_3$, Al forms three single bonds with three chlorine atoms.
• The total number of electrons around the central aluminum atom is $3\times 2=6$ electrons.
• Since aluminum has only 6 electrons in its valence shell, it has an incomplete octet.
• Therefore, AlCl${}_3$ deviates from the octet rule.

B) SF${}_6$:

• Sulfur (S) is in Group 16 and has 6 valence electrons. In SF${}_6$, sulfur forms six single bonds with six fluorine atoms.
• The total number of electrons around the central sulfur atom is $6\times 2=12$ electrons.
• Since sulfur has 12 electrons in its valence shell, it has an expanded octet.
• Therefore, SF${}_6$ deviates from the octet rule.

C) NO (Nitric Oxide):

• Nitrogen (N) has 5 valence electrons, and Oxygen (O) has 6 valence electrons.
• Total valence electrons = $5+6=11$.
• Since NO has an odd number of valence electrons, it is impossible for all atoms to achieve an octet. One atom will necessarily have an odd number of electrons, making it an odd-electron molecule.
• Therefore, NO deviates from the octet rule.

Since AlCl${}_3$, SF${}_6$, and NO all show deviations from the octet rule, the correct option is D.

Correct Answer: (D)