Please tell me....!!

What is the difference between a whip and a top kit.......?!!

technically no difference,both are short poles,it all about length,whips are a fixed length,top kits arn't they're either eth same length as the other pole sections or cut back to suite the elastic used.pole section length is dependant on the makers & how many sections make up the poles desired length two poles off the same length might have a different number of sections therefore differing lengths of those sections the less the section count the longer the sections,the more the section count the shorter the length of the sections (inc top sections)

Top kits are meant to be rigid and go on the end of your pole. Whips are a "rod" in their own right. They are designed to have some flex in them for casting a float and bending when swinging in fish to hand. They can be fitted with a flick tip with the line tied direct, or they can have a hollow tip which can be elsticated if required. Go into a tackle shop and have a waggle, you'll soon notice the difference.

Which would be more suitable for carp margin fishing and what length?

No whip is suitable for carp fishing. You need a strong pole/margin pole with top kits suitable to take elastics from 12+.