Carbocations are stabilized by +I and +R effect.

(i) CH₃—O—CH₂⁺ is more stable than CH₃—CH₂⁺ +I effect of CH₃O- is more than that of CH₃-.

(iii) CH₂=CH—CH₂⁺ is more stable than CH₃—CH₂—CH₂⁺ because former is stabilized by +R effect whereas latter is stabilized by +I effect and magnitude of +R effect is greater than that of +I effect. The resonating structures are as below-

CH₂=CH—CH₂⁺ <----→ ⁺CH₂-CH=CH₂

Therefore, (i) and (iii) are correct statements.