A : Which is the one you like?
B : It's the red one.
A : Which one shall we buy?
B : The red one is cheapest
A : OK, the red one it is!
How would you explain the word order of the final sentence in example B?
This is an example of fronting - ie
This is an example of fronting - iemoving to initial clause position an element normally found in a later position, usually for emphasis.
“Instead of the subject, you can make another element the topic, by moving it to the front of the clause or sentence. …. Fronting gives that element a kind of psychological prominence”.
“In informal conversation, it is quite common for a speaker to front an element (particularly a complement) and to give it nuclear stress, thus giving it double emphasis.”
In this case ‘the red one’ (the complement)is the most important thing as it's the choice the speakers have to make and the ordering of the elements is CSV: complement - subject - verb
Negative adverbs also cause SV inversion if fronted, but in this case the operator is inverted - not the main verb :
Never have I been so embarassed!
Hardly had he spoken, when....