In order to allow the People to exercise their referendum power, no ordinance shall become effective until 30 days from and after the date of its adoption, except, the following, which shall take effect upon adoption:
(a) An ordinance calling for or otherwise relating to an election;
(b) An improvement proceeding ordinance adopted under some law, or procedural ordinance;
(c) An ordinance declaring the amount of money necessary to be raised by taxation, or fixing the rate of taxation; or
(d) An urgency ordinance adopted in the manner provided in this Charter.