What is the ruling on zakat for gold accumulated for marriage or for buying a house, which has reached the nisab, knowing that it is 21-carat jewelry and gold coins, and is it obligatory to convert 21-carat to 24-carat to calculate the zakat?

Zakat on gold must be paid if it reaches the nisab, even if it is prepared for personal use, and its mixture with copper does not harm it. The pure gold content in it must be calculated, and if it reaches eighty-five grams, zakat becomes obligatory on it. You can refer to Fatwa no. 101029 to learn how to calculate zakat on gold of different karats.