Question

which is outermost orbital

Answer 1

Valency and Valence Electrons. The outermost orbital shell of an atom is called its valence shell, and the electrons in the valence shell are valence electrons. ... And, as we stated above in the Aufbau principle, electrons fill lower energy orbitals before filling higher energy orbitals.

Answer 2

Valency and Valence Electrons. The outermost orbital shell of an atom is called its valence shell, and the electrons in the valence shell are valence electrons. Valence electrons are the highest energy electrons in an atom and are therefore the most reactive