Octet Rule states that atoms of main-group elements tend to combine in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. Depending on this fact answer the following question :  *What is an incomplete octet?
*What is an odd-electron molecule?
*Why are there extra electrons in the expanded octet?

First question: The number of electrons surrounding the central atom in a stable molecule is fewer than eight. For example, Boron only needs 6 electrons.

Second question: There are a number of molecules whose total number of valence electrons is an odd number. It is not possible for all of the atoms in such a molecule to satisfy the octet rule. An example is nitrogen dioxide (NO2). Each oxygen atom contributes six valence electrons and the nitrogen atom contributes five for a total of seventeen.

Third question: Expanded octet occurs when an atom is able to have more than 8 valence electrons. For example, in SO₃, the sulfur atom forms 6 covalent bonds, hence it has 12 valence electrons. Expansion of octet is possible only from Period 3 elements onwards, due to the presence of low-lying empty d orbitals that can accommodate the extra electrons.

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Incomplete Octet

In some compounds, the number of electrons surrounding the central atom in a stable molecule is fewer than eight. Beryllium is an alkaline earth metal and so may be expected to form ionic bonds. However, its very small size and somewhat higher ionization energy compared to other metals actually lead to beryllium forming primarily molecular compounds. Since beryllium only has two valence electrons, it does not typically attain an octet through sharing of electrons. The Lewis structure of gaseous beryllium hydride (BeH 2 ) consists of two single covalent bonds between Be and H

Odd-Electron Molecules

There are a number of molecules whose total number of valence electrons is an odd number. It is not possible for all of the atoms in such a molecule to satisfy the octet rule. An example is nitrogen dioxide (NO 2 ). Each oxygen atom contributes six valence electrons and the nitrogen atom contributes five for a total of seventeen.

Expanded Octets

Atoms of the second period cannot have more than eight valence electrons around the central atom. However, atoms of the third period and beyond are capable of exceeding the octet rule by having more than eight electrons around the central atom. Starting with the third period, the d sublevel becomes available, so it is possible to use these orbitals in bonding, resulting in an expanded octet.

Phosphorus and sulfur are two elements that react with halogen elements and make stable compounds with expanded octets. In phosphorus pentachloride, the central phosphorus atom makes five single bonds to chlorine atoms and as a result has ten electrons surrounding it

Explanation:

The answer is c if i’m not wrong

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