Most people think it is on Sunday.......BUT THEY ARE WRONG!
Well not completely.....In recent years, the act of remembrance has been intorduced as a general observance on Armisitice Day (11 Nov). This really didn't happen until quite recently. Until then, the focus was on Remembrance Sunday (the nearest Sunday to 11 Nov), when (as still happens) the ceremony at the Cenotaph in London takes place, and many churches and war memorials across the country hold special services, and include the two minute silence at 11am.
Personally, whilst wishing absolutely to respect the Act of Remembrance (on either occasion), I think too many of these occasions are being introduced, and it is actually damaging the event. I don't mind whether it is 11 November or the nearest Sunday, but it would be better for there to be one common date.