(i) – (a) (ii) – (b) (iii) – (c) (iv) – (d)

Explanation:

in this case the loan pair of the oxygen atom satisfies the positive charge present on the C atom adjacent to O-atom.

And this movement of electrons from the O atom to the C⁺ is called Resonance, hence the given species is stable due to resonance. Hence option (a) is correct match.

in this case we know that the F atom is electronegative atom, hence, it pulls the electrons towards itself and hence it destabilises the C⁺. Hence option (b) is correct match.

in this case, there are 9 alpha hydrogen in the carbanion, hence due to more hyper-conjugative structures the given anion is more stable.

(as more the number of the alpha hydrogen, more is the number of the hyper-conjugative structure.)

in this case, we can see that the carbon having positive charge is attached to the two carbon atoms, and we know that when any carbon atom is attached to the two alkyl groups, it is known as the secondary carbon, and as the secondary carbon is having positive charge, it will be called as the secondary carbocation.