Gold, silver and cash

Wife discharging zakaat on her gold for previous years

Q: I have been married around 15 years, and my wife was give more gold ornaments by their parents! There is zakaat to be given for it and she did not provide it! I don't have any gold or savings! Only my wife's gold! How can I calculate the zakaat for the past 15 years => Gold price was low to high till now. Do I need to calculate the yearly gold rate on that year! Can tell me how to discharge the zakaat for the past years?

Calculating zakaat according to the nisaab of gold and silver

Q: If in 2017 and 2018 a person followed the silver nisab but happened to not pay Zakah in those years despite meeting the silver Nisaab then at a later point (maybe 2018 onwards) he moved to the gold nisaab and when he did calculation for past Zakah, he used the gold nisaab retroactively, even for those years where he followed silver nisaab but that meant for those years he did not owe Zakah according to gold nisaab. Would he be required to still pay Zakah for those two years because at the time of those two years he was following silver nisaab?

Zakaat on gold less than nisaab

Q:

1. I wanted to ask if the only excess wealth a person has is a Kruger coin, is one liable for zakaat as it is less than 87 grams?

2. If a person has the cash that is more than the nisaab and also has gold in the form of 1 Kruger coin only, is zakaat liable on both the cash and the Kruger coin or only the cash?