Is zakat obligatory on an apartment bought in installments with the intention of selling it, given that some installments will remain due after the sale, and how is zakat to be assessed if it is obligatory?

If you intend to sell your share of the apartment for profit, then it falls under trade goods, and Zakat becomes obligatory on it if a hawl (lunar year) passes on its purchase price, provided that the amount reaches the nisab after deducting the apartment's installments.

However, if the purchase was not for trade, but you intended to sell it, for example, to replace it, then there is no Zakat on you.

The nisab for banknotes is the equivalent of 85 grams of gold or 595 grams of silver, and the obligatory Zakat is a quarter of a tenth (2.5%).