it should be "what will be happening?" (future progressive form) that describes an ongoing or continuous action that will take place in the future. always used with "will be" or "shall be", with the verb form ending in 'ing'. "what will happen?" (future tense) that expresses an action or situation that will occur in the future. :)

If ice (be )...........heavier than water , it ( not float ).......

Hello Donna, I'm in complete agreement with Rainbow and Romulus, but I wanted to add a quick note about "be" in compound tenses which, I hope, will help you avoid having similar uncertainties in the future. Generally speaking, there are four forms of the verb in English V1 (the base form), V2 (the preterite or past tense form), V3 (the past participle) and Ving (the present participle and gerund). Of these four forms, you can only ever use V3 or Ving after "be" in a compound tense. This means that "what will be happen", i.e. "will be + V1", is ipso facto incorrect. "Be + V3" is used to form passives, while "be + Ving" is used to form continuous/progressive tenses. Hope this helps, Alvin

The first is not crrect