1

Can two blocks have the same Previous hash after being created.

2 blocks totally different from each other but with the same previous hash

3

Can two blocks have the same Previous hash after being created.

Yes, two otherwise valid blocks could be created that both link to the same parent block, but importantly: only one of those two blocks will become a part of the valid chain. So ultimately, only one of them will be valid, and the winner will be the block that miners build on top of first (and thus it becomes a part of the longer chain).

The other block will become what is called an 'orphan block' (though some people prefer the more exact term, 'extinct block').

You can look through the tag for more info.

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  • What happens to the transactions on the orphan block? – Juan Feb 20 '19 at 23:11
  • @Juan simply: they are no longer a part of the blockchain record. – chytrik Feb 20 '19 at 23:12
  • So that money is gone for good? The money X person sent to z person no longer exists? – Juan Feb 20 '19 at 23:12
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    @Juan no, the bitcoin would still exist, but the transaction sending it from X->Z would not (unless that transaction is also confirmed in the longest valid chain). – chytrik Feb 20 '19 at 23:14
  • Oh okay, so you would have to send the transaction again so Z can get it – Juan Feb 20 '19 at 23:15

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