Increasing order of the following stability is:
(a) I > II > III > IV (b) I > III > II >IV
(b) I > IV > III > II (d) IV > III > II > I
Here all alkenes are equally substituted (disubstituted) so we need to check hyperconjugation effect with the pi electron density .This depends on the number of H atoms on the carbon(sp3) bonded to sp2 carbon of the double bond.
Structure I --3 Hs for hyperconjugation
Structure II --2 Hs for hyperconjugation
Structure III --1 H for hyperconjugation
Structure IV -- none H for hyperconjugation