All of Palestine was allocated to the Jewish People with the San Remo Resolution on April 25, 1920 at the San Remo Peace Conference. The Arabs have civil and religious rights -- not political rights.
Who told you that?
The legal title of the Jewish People to the mandated territory of Palestine was first recognized under international law on April 24, 1920 when the Supreme Council of the Principal Allied Powers, consisting of Great Britain, France, Italy and Japan decided to approve the Balfour Declaration of November 2, 1920 (thereby giving international legal effect to its provisions) and incorporate Article 22 of the Covenant of the League of Nations.
As a direct result of the Allied Supreme Council decision on April 24, 1920, the San Remo Resolution of April 25, 1920 -- which is the basis for the Mandate for Palestine -- the title of sovereignty over Palestine was exclusively vested in the Jewish People and not in any other nation, state or entity.
Here's the relevant paragraph of the San Remo Resolution (April 25, 1920) text:
The High Contracting Parties agree to entrust, by application of the provisions of Article 22, the administration of Palestine, within such boundaries as may be determined by the Principal Allied Powers, to a Mandatory, to be selected by the said Powers. The Mandatory will be responsible for putting into effect the declaration originally made on the [2nd] November, 1917, by the British Government, and adopted by the other Allied Powers, in favour of the establishment in Palestine of a national home for the Jewish people, it being clearly understood that nothing shall be done which may prejudice the civil and religious rights of existing non-Jewish communities in Palestine, or the rights and political status enjoyed by Jews in any other country.
San Remo conference - Wikipedia