Does zakat become due on an apartment purchased in installments for residential purposes, with the intention of selling it if a good opportunity arises?

If you intend to sell it at a price you are content with, then it is a trade asset on which zakat is obligatory, even if you intend to live in it temporarily before selling; because the intention to sell makes it a trade asset. However, if you are hesitant about selling it, then there is no zakat on it.