Answer:
Isolated gaseous atom
56Ba
Explanation:
The word isolated means seperate or kept apart .
When an atom is free from other atoms in gaseous state, is called as "isolated gaseous atom".
The lowest energy state possible for an atom is ground state.
The electron configuration of an atom is the arrangement of electrons distributed among the orbital shells and subshells the electronic configuration is used to describe the orbitals of an atom in its ground state
1.The configuration for the free atoms is:
Ba - [Xe] 6s²
Br - [Ar] 3d¹⁰4s²4p⁵
S - [Ne] 3s²3p4
Si - [Ne] 3s²3p²
Thus:
Answer is A
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