1. Recall that the vibrational eigenfunctions of a harmonic oscillator are
orthogonal:
If yj and yk belong to different electronic states as shown here, is
this still true?
(A) Yes, because two vibrational eigenfunctions are always orthogonal.
(B) No, because the potential curves are anharmonic oscillators, and two eigenfunctions of anharmonic oscillators are no longer orthogonal.
(C) No, because they belong to different oscillators (different el. curves)

2. Recall that the vibrational eigenfunctions of a harmonic oscillator are
orthogonal:
If yj and yk belong to different electronic states as shown here, is
this still true?
(A) Yes, because two vibrational eigenfunctions are always orthogonal. No, see (C)
(B) No, because the potential curves are anharmonic oscillators, and two eigenfunctions of anharmonic oscillators are no longer orthogonal.
Not true! Any two non-degenerate eigenstates of the same system are orthogonal.
(C) No, because they belong to different oscillators (different el. curves).
Orthogonality is only given within one and the same curve.