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If I understand it correctly, a transaction must be included in a block and broadcasted to other nodes before the transaction is accepted as valid. But it takes time to create such a block which only miners create.
How much time does it take before the transaction is registered as valid?
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Ok how long time does it take before the transaction is registered as valid?
Depends on the transaction fees, the no. of transactions at that time, etc.
And how much is the miner rewarded for creating that block?
The block reward right now is 12.5 BTC and the transaction fees.
How many transaction can there maximum be in a block?
Varies w.r.t. the transaction. On average (as of Nov 2017) 11K+ per hour (Source)
The difficulties increases all the time. Will we reach a point where it is impossible to create blocks (=The end of bitcoins)
The difficulties increase because the mining power is increasing. If there comes a point where the miners drop out due to increase of difficulty, then the difficulty decreases within 2 weeks. It will decrease in such a way that to make it an average of 10 minutes to mine a block.
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Time between mining the blocks is around 10 minutes. Bitcoin protocol adjusts itself to keep that 10 minutes target.
But the transaction is not necessarily included in the next block. It depends on the number of transactions and fee you provide to incentivize the inclusion of your transaction. If the fee is too low transaction will never be mined (put in the block and added on blockchain). If the fee is reasonably high it will be included in the next block (so less than 10 minutes time).
The party receiving the money should not consider transaction valid up until it is "buried" under a number of other blocks (let's say 6 - so another 60 minutes after your transaction is added on the blockchain).
This is a better answer IMO because it recognises the OP's desire at how long it takes a transaction to be "valid" - a term that has a large degree of subjectivity within a block-chain. For some people/companies, even transactions 10 block levels deep might not be valid if they have only 1 confirmation (unlikely scenario but nonetheless possible!) – GrayedFox – 2018-03-08T00:05:27.677
1You should post those as separate questions and first check if it is already answered somewhere before. – croraf – 2017-11-04T11:24:30.557