Quorum requirements for a referendum to be valid

Ukraine

Answer

Mandatory referendum - turnout quorum
Optional referendum - turnout quorum

Source

Law of Ukraine onall-Ukrainian and Local Referendums

http://www.legislationline.org/documents/action/popup/id/7114

ARTICLE 41.

[…]

Thereferendum shall be considered not to be conducted if less than 50% of thecitizens on the voter list participated in voting, and a referendum on pre-termtermination of the authority of the Verkhovna Rada of Ukraine and the Presidentof Ukraine shall be considered not conducted if less than two-thirds of thecitizens on the voter list participated in it.

Comment

50% or 2/3 of electors depending on issue (see quotes)