Question

which is the largest thing in the universe?

Answer 1

   Your question has no answer choices what so ever. I suggest putting some down so we could break it down and simplify it, but based on my research, there are multiple objects that are the 'largest' thing in the universe, specifically, an object after the big bang occurred. If you search it, it says it's 2 million light years away, but other galaxies hold planets known as the 'largest object.'
   One of the 'largest' and known things, is the 'expanding galaxy' itself.
it just keeps on expanding, creating more sources, and objects, breaking down matter. So I'm sure there are multiple of which we haven'r even explored, so as to your question, I can't say much. 
Thanks!

Answer 2

For our earthly relevance, it would be the brightest star you can see without binoculars and is not a planet. There are bigger ones, but you need a technologically sophisticated telescope to find them. There are bigger ones than even those, but we don't have the technology to "see." I would have to say, consequently, that we do not know. Nor may we ever know.