A sample of allyl chloride contained a significant amount of an impurity. The impurity was isolated using distillation technique and a ¹³C-NMR spectrum of the impurity was obtained.

If the molecular formula of the impurity is C₃H₆O:
(i) Give a plausible structure for the impurity.
(ii) Assign all peaks in the ¹³C-NMR spectrum of the impurity.
(iii) Explain how the impurity arose in the sample of allyl chloride.