How is Zakat on money calculated for amounts from selling a car and buying gold bars at different times, with a pre-existing gold bar, all for the purpose of buying an apartment?

First: There is no zakat on a car unless it was purchased with the intention of trade. The hawl (zakat year) for the zakat of its price begins from the day it is sold. However, if it was purchased with the intention of trade, the hawl begins from the day the money with which it was bought was acquired.

Second: If gold ingots were purchased with the money, the hawl remains as it is, because the hawl is not interrupted by exchanging money for gold, silver, or trade goods. When its hawl is due, its zakat is obligatory at one-quarter of one-tenth (2.5%) of its weight or value on the day of zakat, unless an apartment for personal use was purchased with it. If an apartment for trade was purchased with it before the hawl, the hawl is not interrupted, and its zakat becomes obligatory by evaluating the apartment and paying one-quarter of one-tenth of its value.

Third: The hawl for the father's money begins from the day it was received. There is no zakat on it if it was used as part of the price of an apartment for personal use before the hawl was complete.

Fourth: For the ten-gram ingot, it is necessary to know its hawl, which is the hawl of the money with which it was purchased. There is no zakat on it alone due to it not reaching the nisab (minimum threshold), unless other money is combined with it that makes it reach the nisab. In the third year, since you have a nisab of cash, you are required to pay zakat on the ten grams if its hawl was on or before Safar 28, and you had not previously used it as part of the price of an apartment for personal use. Gold is combined with silver and cash to complete the nisab.