if someone gets a purpose of trip (one year in advance)..can they apply for the B1/B2 Visa from now?
Technically you can apply for B1/B2 visa one year in advance of your trip, however then your acceptance or rejection of your visa will not depend upon the proposed trip, but your general eligibility.
you have to understand that VISA counselors will think that a lot can happen in a year like:
1. Trip getting cancelled
2. purpose of visit changing
3. other restrictions that may occur.
so basically if you apply right now, they will try to judge if you are a potential immigrant or NO. your intended trip will have no weight.