What is the order in which UTXOs are sorted in a block? Let's say, I am trying to do a double spend by creating two transactions almost immediately, is it possible that both the transactions are added in one block ? If yes, then which transaction is valid and which is invalid ? Also is there any specific order in which miners gather transactions in a block before starting to find proof of work ?
Addition to Bolton's answer: Transactions in a block can be in any order, given that if a transaction spends another's output, the parent transaction must come before the child tx and the coinbase transaction (collecting the block reward) comes first.