Why do valency electrons involve in bond formation , than electrons of inner shells ?

Explanation

1) When two atoms come sufficiently close together the valence electrons of each atom experience the attractive force of the nucleus in the other atom.
2) The nucleus and the electrons in the inner shell remain unaffected when atoms come close together.
3) The electorns in outer most shell of an atom get affected.
4) Thus electrons in valence shell are responsible for the formation of bond between atoms.