POST ON MULTIPLE GROUPS IN ONE CLICK IN FACBOOK

STEP 1:
First of all visit to this website.

STEP 2:
Now click on LOGIN and you'll get app page, just ALLOW THE APP TO POST ON YOUR BEHALF. 

STEP 3:
After that you'll get back on website, here just fill the empty fields and select the groups on whch you want to post, after that just Click on post.