Is Zakat due on money invested with a merchant, and how is its value calculated, and are outstanding debts and Murabaha installments deducted when it is disbursed?

Whoever possesses wealth that has reached the nisab (minimum threshold) – 85 grams of gold or 595 grams of silver – and upon which a full lunar year has passed, must pay zakat on it. This includes wealth invested in trade. The zakat amount is 2.5% of the total capital and remaining profits. Regarding debts, the majority of scholars believe they should be deducted from the wealth subject to zakat. However, Imam Al-Shafi'i, in his later opinion – which is the more cautious view – believes they should not be deducted. If there is non-zakatable wealth exceeding one's living needs, it should be set aside to cover the debts. If it equals or exceeds the debts, nothing is deducted from the debts. If it is less than the debts, the remaining amount is deducted.