Explain valence shell and penultimate shell

Explanation:

The valence shell is an atom's outermost shell that contains electrons. It could be completely full, half-full, or somewhere in the middle.
Valence electrons are electrons that exist in these valence shells.
The electrons in valence shells govern how an atom will combine with other atoms.
The number of valence electrons is used to calculate valency.
The penultimate shell is the shell that is filled just before the valence shell, that is, the shell that is just inside the valence shell.
It will be one less than the valence shell.
If the valence shell has the value 'n,' the penultimate shell will also have the value 'n.' (n-1).

Final Answer:

The valence shell is the final shell of an atom that contains valence electrons.
This shell is also referred to as the Ultimate shell.
The shell immediately preceding the valence or the ultimate shell is known as the penultimate shell.
Specifically, the atom's second last shell.