How is the obligatory Zakat determined for a sum of money inherited from a father, which has reached the Nisab, but it is not known when it reached the Nisab or how many years have passed on it, considering that it accumulated over years, and this is prior to its distribution? And what is the amount of Zakat?

Zakat on banknotes is estimated by silver, not gold. The nisab for silver is 595 grams. So, whoever possesses this amount and a hawl (lunar year) passes while it is in their possession, zakat becomes obligatory on them. If the father did not pay zakat during his lifetime, it becomes a debt upon him that takes precedence over the distribution of the inheritance. One-quarter of a tenth (2.5%) must be paid for each year, estimated based on his wealth.