Second question, is a transaction with 1 confirmation reversible? What are the chances of 1 confirmation Bitcoin reversible?
Some wallet has varying amount of confirmations needed before a transaction is spendable. But it usually takes up to 3 confirmations on a standard Bitcoin wallet before you can spend it. I think for electrum one confirmation can be spendable and the higher the number of confirmations you get on your transactions, the lesser the risk of it being reverted or double spent.
For exchanges, they require 1 confirmations to get your Bitcoin deposited and you would be. Able to spend them.( Also depends on the wallet address type you used on the exchange).
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1 confirmation: sufficient for small payments less than $1,000.
3 confirmations: for payments $1,000 - $10,000. Most exchanges require 3 confirmations for deposits.
6 confirmations: good for large payments between $10,000 - $1,000,000. Six is standard for most transactions to be considered secure.
10 confirmations: suggested for large payments greater than $1,000,000.
3 confirmations: for payments $1,000 - $10,000. Most exchanges require 3 confirmations for deposits.
6 confirmations: good for large payments between $10,000 - $1,000,000. Six is standard for most transactions to be considered secure.
10 confirmations: suggested for large payments greater than $1,000,000.
read here =How many Bitcoin confirmations is enough?
The chances of transaction being reversible is calculated using the risk formula on the bitcoin whitepaper.
Where
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q=probability of the the next block being mined by the attacker
p=probability of the next block being mined by honest miners
Z= number of confirmations your transaction has received so far.
p=probability of the next block being mined by honest miners
Z= number of confirmations your transaction has received so far.