There are multiple important aspects to take into consideration when assesing the quality of an online source, specially when writting a historical reasearch paper, since facts like dates and places must be accurate.
From the presented options clearly the first one is the most relevant one, evaluation the source's objectivity. This can be accomplished by analyzing different aspects of the text. One of them is the language used, is it exagerated? Does it present multiple negative adjectives or multiple positive ones? Another important factor to consider is the presentation of both sides of the historical event. If the source only presents one of the implicated side's point of view, it is evidence of a biased perspective which may cause the information to be inaccurate or imprecise. Finally, it's important for the source to quote it's sources so one can check how diverse they are and how trust worthy one may consider them. If an article quotes academic studies from around the world, first hand sources and historians thesis, it's most probably a reliable source.