Is Zakat obligatory for the past and coming year on a sum of money set aside for purchasing an apartment, given that there is an issue with finalizing the contract and a decision has not been made whether to proceed or withdraw?

The mentioned amount remains in the possession of the questioner, and he must pay zakat on it for the past and current year if it remains with him, whether he enters the project or not. If he pays the amount to the entity owning the project, then it leaves his possession and zakat is not obligatory on him. As for purchasing an apartment with deferred payment, there is a difference of opinion regarding the effect of debt on the obligation of zakat on wealth.