According to all dictionaries I can see and everyday use by native speakers, this is the correct way:
On the one hand, it’s larger; on the other hand, it’s more expensive.
What makes no sense to me instinctively is the use of the first the. What is the one hand? Shouldn’t it be just one hand?
Is this a grammatically valid construct I just don’t understand, or is it an idiom that has changed to improve the presentation of the comparison described? It arguably sounds better with the additional the.
The definite article is used to signal that one is talking about specific items, not items in general.
For example, this exchange at the reception desk of the hotel.
Guest: I’d like a room.
Clerk: Will you be staying the weekend, sir?
Guest: No, just the one night.
The guest could have said “No, just one night,” but adding the definite article makes it more emphatic and specific at the same time. This applies to “on the one hand” constructions as well.
Source : Link , Question Author : Pekka , Answer Author : Robusto supports Ukraine