Question

The octet rule is not valid for which one of the following molecules?

• A. CO\(_2\)
• B. H\(_2\)S
• C. NH\(_3\)
• D. BF\(_3\)

Hint:

Electron-deficient molecules like textbfBF(3) and textbfBeCl(2) do not follow the octet rule.

Answer 1

The Correct Option is D

Step 1: Recall the octet rule. The octet rule states that atoms tend to combine in such a way that they have eight electrons in their valence shell. Step 2: Examine each molecule.

CO\(_2\): Carbon forms two double bonds with oxygen. Carbon and oxygen both complete their octets. ✔
H\(_2\)S: Sulphur has eight electrons around it (two bonding pairs and two lone pairs). ✔
NH\(_3\): Nitrogen has three bonding pairs and one lone pair, completing its octet. ✔
BF\(_3\): Boron forms three bonds and has only six electrons in its valence shell, not eight. ✘
Step 3: Final conclusion. The octet rule is not satisfied in BF\(_3\). \[ \boxed{\text{(D)}} \]