What do you mean by pseudo noble gas configuration?

Pseudo noble gas configuration refers to a stable electron arrangement that resembles noble gases but includes a completely filled d-subshell along with the outer s and p orbitals. Noble gases are very stable because their outermost shell is completely filled. 

Other elements try to achieve this stability by gaining, losing, or sharing electrons. Sometimes, instead of achieving exact noble gas configuration, elements gain stability by filling the d-subshell as well. This is called pseudo noble gas configuration.

Definition

An atom is said to have a pseudo noble gas configuration when it has completely filled outermost s and p orbitals along with a filled (n–1)d orbital. This makes the atom stable, even though it is not a true noble gas.

Examples

• Cu⁺ (Copper ion): Electron configuration [Ar] 3d¹⁰.
• Ag⁺ (Silver ion): Electron configuration [Kr] 4d¹⁰.
• Au⁺ (Gold ion): Electron configuration [Xe] 4f¹⁴ 5d¹⁰.

Difference Between Noble Gas and Pseudo Noble Gas Configuration

Importance

• Explains stability of transition metal ions.
• Helps understand chemical bonding in d-block elements.
• Shows why certain ions are more stable than others.