Dear NT:

You wrote:
> Are these sentences correct:
> 1-There is something which it is necessary for us to consider.
> 2-This is something which it is necessary for us to consider.
> 3-There is a man to whom it might be good to talk.
> 4-He is the man to whom it might be good to talk.
>
Sentences 1 and 2 are not correct. Which as the relative pronoun is also the subject of the subordinate clause. Both sentences should read “which is necessary for us to consider.”

3 and 4 are both OK, though perhaps a bit awkward in normal speech. It is appropriate when corresponding with individuals who are sensitive about ending sentences with prepositions. Most people would say, “He is the the man it might be good to talk to,” with or without the whom.