Quorum requirements for a referendum to be valid

Italy
Answer
Optional referendum - turnout quorum
Source
Constitution of1947 with Amendments through 2012
https://www.constituteproject.org/constitution/Italy_2012.pdf
Art75
[…]
Thereferendum shall be considered to have been carried if the majority of thoseeligible has voted and a majority of valid votes has been achieved. Theprocedures for conducting a referendum shall be established by law.