Yes, unfortunately #2 is completely correct. You seem to have become slightly confused about the order of events in this excellent epic. The reasons for Grendel's anger are of course never disclosed to us in the text. Please use the study guide of enotes to remind yourself once again of the plot, and then if you need to reword your question, we will see if we can help.
Your question does not match the events of the story, I'm afraid. Beowulf comes to Hrothgar's aid and battles with Grendel, eventually killing him. Grendel's mother comes back to Hrothgar's Hall (Heorot) to retrieve her son's arm and Beowulf follows her, eventually killing her, as well. There is no searching for Grendel by Beowulf--or anyone else, for that matter--and Beowulf does not feel angry. If you mean why does Grendel feel angry, the story says he "nursed a hard grudge" against Hrothgar and Heorot, but that's about all we know.
Well After finding the Mystic Sword and cutting off Grendel's mother head off. Beowulf wanted to get his full revenge because he was still angry with Grendel killings. So he finds him and cut off his head too. To bring it home to the king.
Actually number 1 is right.I have here my question, as it is written like number 1 put it.My school is the one who wrote it that way.Not us, and if you think we are confused just imagine how we feel when we look for help and thats the answer we get.We are not the confused ones.You are.We are looking for help.