Zakaat

Zakaat on land purchased with the intention of resale

Q: A person purchased land abroad with the intention to sell and make profit 8 years ago. The price of this land has risen, thought is stagnant at present. However due to a decline in foreign investors in the country the market for foreign companies purchasing land from individuals is at a standstill. Therefore being unable to sell this land for the foreseeable future would one be required to pay zakaat on this? If so, at what price? i.e market or purchase price?

Discharging zakaat for previous years

Q: Until recently I thought I did not have to give zakat because I was under the assumption there was only one nisab, the nisab for gold, and I have never owned more than the nisab for gold. However now I am aware that there is a nisab for silver, and that this should be used when calculating zakat. Since I haven't paid zakat until now, I would like to start calculating my zakat for the previous years as well as for this year however I have some questions as I haven't calculated zakat before:

1) Do I estimate how much zakatable assets I have at the END of each zakat year and then pay 2.5% of that in zakat?

2) The nisab value constantly changes, for example at the moment the nisab for is around £294, but previous years it was different. So when determining if I own above the nisab in previous years and am therefore eligible for paying zakat, since I don't know what the nisab was in those years should I use the current nisab when calculating for previous years?

3) Since I did not know I had to pay zakat, I also have not taken part in qurbani (udhiya). How should I go about calculating how much I owe for this?

4) Can I pay my zakat through an islamic charitable organisation, such as MuslimAid, IslamicRelief, etc?

Forgive me for the long question, but I want to make sure i'm paying zakat correctly, especially as I had been ignorant of it for many years. May Allah subhanahu wa ta'ala make it easy for us to fulfil our religious obligations.

Which value will be considered for gold and silver jewellery?

Q: The general "market" for an ordinary person wishing to sell his jewellery in our times would be to a jeweler or a gold purchaser. The value thus given by them constitutes the market value. The established practice of both these dealers in evaluating an item to be purchased by them is to consider the gold content present in the jewellery only. They ignore any value that may exist due to the workmanship present in that gold or silver jewellery.

Question: Will this value given by the jeweller or gold purchaser (which is based on gold content only) be the market value considered for zakaat purposes?