The correct option is C (ii)>(i)>(iii)
In structure (i):
There is no resonance taking place, it is only stabilized by hyperconjugation due to presence of α-hydrogens.
In structure (ii) :
Even though it has less α-hydrogens than structure (i), this structure is stabilized by resonance. So, it is more stable than structure (ii) because resonance effect is more dominating than hyperconjugation.
In structure (iii) :
This structure is planar, is cyclic, has conjugation and has 4 π e− thus making it anti aromatic. Since anti-aromatic structures are the least stable. So, correct order of stability is : (ii)>(i)>(iii)