In the prepositional phrase : "Who did you give your number to?" Is the TO at the end of the sentence absolutely necessary?
The verb give participates in something called the Dative Alternation:
I gave the book to him.
I gave him the book.
Both of these sentences can be used with the same meaning. Levin gives the following examples of verbs that participate in the Dative Alternation:
- give-type verbs: give, hand, lend, loan, rent, sell, . . .
- send-type verbs: send, mail, ship, . . .
- throw-type verbs: fling, flip, kick, lob, slap, shoot, throw, toss, . . .
But the example I've given above is very simple. If we make things more cognitively complex by making the example interrogative, then we find a strong preference for the version that is explicitly marked by a preposition. Why?
In Cognitive complexity and increased grammatical explicitness in English, Günter Rohdenburg outlines his Complexity Principle, "explicitly marked phrases are preferred over zero-marked counterparts in cognitively complex environments". Following this principle, it seems many speakers have a strong preference for including to in the interrogative version:
Who did John give the book?
Who did John give the book to?
I personally find both versions grammatical, but I think you'll find that people usually choose to include this preposition in real life examples.
The preposition is required to link who to the verb. If you omit it, it would be like omitting it from this sentence
I gave my number to Joe (correct).
I gave my number Joe (incorrect)
Note that it is permissible to omit the to for this type sentence by inverting the order of the direct object (number) and the indirect object (Joe):
I gave Joe my number (correct).
It is not, however, possible to omit the preposition from your sentence:
Who did you give your number to?
Strictly speaking, to requires an accusative whom, but in spoken english most people say who in a sentence like this.