Question

what is penultimate shell ..,.​

Answer 1

The outermost shell (shell-3) of an atom is called valence shell while second last shell (shell-2) is called penultimate shell and the 3rd last (shell-1) is called Ante-penultimate shell

Answer 2

The shell which is before the valence shell is called penultimate shell. If 'n' is the valence shell then (n-1) is the penultimate shell. Transition elements contain unpaired electrons in penultimate shells

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