Can a unconfirmed transaction be lost or modified?

Question

I am beginner and I am still learning fundamentals of block and bitcoin network.

Suppose, I do a transaction on bitcoin network, it is marked as unconfirmed transaction and is stored in mempool of full nodes.

This unconfirmed distributed over network, at some point a minor will create a block which will contain this transaction.

My question is where these unconfirmed transactions are stored before being included in block or hence block chain?

Can they be modified before a minor put them in blockchain?

Answer 1

where these unconfirmed transactions are stored before being included in block

Mempool

Each node (wallet, miner, etc) stores them in a local collection called the "mempool". The name implies these are typically kept in memory (RAM) but the developers of each wallet software can decide whether to also store the data onto non-volatile storage such as disk.

Can they be modified before a [miner] put them in blockchain

No, because they are each signed

Modifying the transaction would make the transaction signature fail verification. Only the person who knows the secret number known as a private key can produce a valid signature for a transaction. The inputs to a transaction are locked by a script that can only be satisfied by a number resulting from the use of the private key.

Every other node (wallet, miner etc) would reject a modified transaction and start to suspect the source as being potentially malicious.