(a)   I < II < III (b) II < I < III ( c) I < III < II (d) II < III < I

More substituted alkenes are more stable -Zaitsav's Rule This is due to the fact that pi electron density of alkene is more stabilized as it undergoes more hyper conjugation  with neighboring Carbons H atoms.More dispersal of charge ,more is the stability.
In this example i) Disubstituted ii)Trisubstituted and iii)tetrasubstituted