What is the ruling on Zakat for land that has been owned for a full year, but its owner's intention regarding it did not become firm until the end of the year, at which point he decided to sell it?

Land purchased for purposes other than trade is unanimously not subject to zakat (definition). A mere intention to sell it does not necessitate zakat until it has been sold, its price received, and a full year has passed on that amount. As for land purchased for trade, zakat becomes obligatory on it when a full year passes, provided its value reaches the nisab (definition), based on the hadith (definition) of Samurah: "The Messenger of Allah, peace and blessings be upon him, used to command us to give sadaqah (definition) from what we prepared for sale." In cases where the intention oscillates between trade and personal use, the stronger intention prevails.