Minxxxx
In EU OPS you can dispatch with no alternate, provided certain conditions prevail, such as VMC at destination, less than 6 hour flight, two runways with independent approach procedures... Most MOs make mandatory to name an alternate anyway, but some airlines make use of that rule and take off with no alternate fuel reserve.
Normally you will name one alternate, except if the destination airport is below minima or you don't have destination WX forecast for ETA +-1 hour. In these cases you have to name two alternates, and the alternate fuel reserve is the greater of both.