Who can initiate an optional referendum at the national level?

Hungary'sConstitution of 2011

https://www.constituteproject.org/constitution/Hungary_2011.pdf

National referenda

Article 8

1. Parliament shall order a national referendum upon the motion of atleast two hundred thousand electors. Parliament may order a national referendumupon the motion of the President of the Republic, the Government or one hundredthousand electors. The decision made by any valid and conclusive referendumshall be binding on Parliament.

2. National referenda may be held about any matter within Parliament’sresponsibilities and competences.

[…]

4. A national referendum shall be valid if more than half of allelectors have cast a valid vote, and shall be conclusive if more than half ofall voters casting a valid vote have given the same answer to a question.

The President of the Republic

Article 9

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3. The President of the Republic:

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d. may propose national referenda,

e. shall set a date for the general elections of Members of Parliament,local representatives and mayors, and of members of the European Parliament,and for national referenda,

National Election Office (website)

http://valasztas.hu/en/ovi/287/287_0.html

The followingentities may initiate national referendum:

a) citizenseligible to vote,

b) the Presidentof the Republic,

c) theGovernment,

d) at least onethird of the elected MPs.

If the referendumhas been initiated by the entities referred to in items b), c) and d), thelaunching of a national referendum is subject to the weighing of the NationalAssembly.

It is importantthat the entities initiating a referendum have to make proposal on the wordingof the question(s) subject to the referendum.