Is Zakat obligatory on the full price of the house (500,000 Riyals) or on the remaining amount after deducting the debt (400,000 Riyals), knowing that the debt has not yet been paid off?

A house designated for personal use is not subject to zakat merely by the intention of selling it. Rather, once it is sold, its price should be held for a full year from the day of sale [before zakat becomes due]; because a mere intention to sell does not transform an asset into a trade commodity according to the majority of jurists. However, if the house was acquired with the intention of trade, then it becomes a trade commodity, and its value is assessed when its [zakat] year is due. If its value reaches the nisab, zakat is paid on it by giving one-quarter of one-tenth in cash.