Is zakat due on an apartment that has not yet been finished or inhabited, and three years have passed with the intention of renting it out? And is zakat due on a private car that is used?

The rented house is not subject to zakat on its value. Zakat is only obligatory on the rent received if it reaches the nisab by itself, or when combined with other money or trade goods, and a year has passed over it. As for a private car, there is no zakat on it because it is not among the zakatable assets intended for growth. The Messenger of Allah, peace and blessings be upon him, said: "There is no sadaqah (zakat) on a Muslim for his slave or his horse."