Could be a pastry tip. There are four shapes that measure about 2" long, with a 3/4" diameter opening. Round Tip, Star Tip, Closed Star Tip, French Tip. The cupcakes in the picture are mini cupcakes, so any of these could work. I use a 1M for my cupcakes...another possibility.
Counting the ridges, I'd say 2E or 1C.