Gold, silver and cash

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?

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?

Q: My wife has around 17 tola gold. I want to know how much zakat she has to pay on it? 

Q: If a person has a gold tooth, will it be necessary for him to include it in his zakaat calculation and pay zakaat on it?

Q: If jewellery is of unknown metals (unknown carat for example), how do we pay zakaah on it if there is no indication of what it is? If it's gold in colour but unknown what it consists of.

Q: My wedding jewellery set is now lost for two years. Until last year, I paid zakaat on it thinking that I would find it. At present, it is still lost. Should I continue to pay zakaat on it?

Q: A person bought 250 grams of gold in Dec 2016 and was unable to pay zakaat during the last 4 years. Now he wants to make up for the missed zakaat.

The question is, should he calculate the due zakaat of all 4 years on the current gold rates? Or should he calculate 2017 zakaat on 2017 gold rate, 2018 zakat on 2018 gold rate and so on? 

Q:

1. Suppose if I have 75 grams gold, 750 grams silver and some cash in hand and bank. Do I have to calculate separate zakaat of all items or calculate total zakaat.

2. If I have 85 grams gold it is zakaatable. But I have only 75 grams is this gold exempted from zakaat?

Q: I have 3 tolas of gold and one year passes over it. Is zakaat liable on me or not?

Q: I have about 25 tola gold۔ I want to know the zakaat in rupees.