Where does the 2015 Nepal earthquake rank amongst earthquakes since 1900?
About 80th.

I counted the earthquakes of each magnitude on the List of deadly earthquakes... article. If the Nepal earthquake is about M7.8, then it's in the range 69th to 86th on that list:



Note that there are more earthquakes than this in recent history, the list has already selected for deadliness. Also note the point in the comments about different magnitude measures in the list, and the fact that the list is a few years out of date. I don't think these things change the answer.