Sending BTC using Seed Hex or mnemonic

I’m interested in sending BTC from wallet to another and probably automate it through some libraries.

I have a question: if I have a seed hex or 12 words I can generate all my wallets (addresses, private keys) with BIP39 mnemonic tool.

How could I know what of external wallets (private keys) I should use to send btc using libraries assuming it usually changes?

How could I basically send BTC to some wallet having only seed hex or 12 words?

recover wallet in electrum from hex mpk

I´m trying to recover a wallet from which the Master Private Key (mpk) in hex format and the number of used addresses is known.

Till now I could manage to convert the hex mpk to the wif format and import this to electrum. But here to history seems to be totally lost.

Is there any way to recover the full wallet and history (not neccessary with electrum)?

How to fetch incoming transaction in Ripple

Currently I have setup ripple mainnet server and provide availability of XRP trading, If any user submits the transaction in his account from the external wallet, How I know which transaction performed? Currently, I have used WebSocket socket and subscribe all account to the listener, So when any transaction comes in subscribed account then it will catch the transaction. But the issue is that when my xrp server is down or listeners missed any transaction then how we fetch incoming transaction later.

Where exactly is the scarcity?

In discussions on the intrinsic value of BTC, one often reads the claim that BTC is scarce because the maximum amount of BTC that can ever exist is 21 million BTC. I find this explanation rather unsatisfactory.

If a group of people collectively decide to move all their savings into tulips, the price of tulips should skyrocket. However, new greenhouses could be built and some farmers could start growing tulips. As a result, the price of tulips would start falling and converging to the price prior to the "tulip mania". Seeing the value of their savings dropping, these disappointed tulip-lovers would rush to sell their tulips, causing the price of tulips to plummet. The media would then mock them for their financial illiteracy. It’s hard out there for a tulip-lover…

If the former tulip-lovers then decided to move their savings into gold, the price of gold would almost certainly rise suddenly. However, new gold reserves cannot be manufactured out of, say, lead — assuming that no form of working alchemy is developed, of course. Without the required increase in the supply of gold, the price of gold would stay relatively high and there would be no panic-selling. A computer scientist would perhaps say that the supply of gold is rate-limited.

I know nothing about economics, but I suppose an economist would say something along the lines of "the supply of gold is much more price-inelastic than the supply of tulips". To me, BTC looks closer to digital gold than to digital tulips.

Questions — As a total novice, the scarcity pertaining to BTC I do see is in the rate at which new BTC can be generated. But, what exactly does that have to do with the number 21,000,000? When mentioning the total amount of Bitcoin that can ever be mined, shouldn’t the practical upper bound on annual mining also be mentioned? Is my understanding of "Bitcoinomics" roughly accurate?

What’s a unique identifier in listsinceblock output?

I am trying to understand if there a unique identifier for transactions. I didn’t find anything about that mentioned in listsinceblock‘s help.

{
  "involvesWatchonly": true,
  "account": "",
  "address": "mvd6qFeVkqH6MNAS2Y2cLifbdaX5XUkbZJ",
  "category": "receive",
  "amount": 10,
  "label": "",
  "confirmations": 69,
  "blockhash": "62967ce950fc03b14179e58f42e426b63cbfbf63c2b9e59acb6a719a09c23b94",
  "blockindex": 58,
  "blocktime": 1524872287278,
  "txid": "aac9b2d7bb7b3476a83a5ac0c2fe21625bcd961ed43a5c5fd3eacf6536dc81d5",
  "vout": 7,
  "walletconflicts": [],
  "time": 1524872276635,
  "timereceived": 1524872276635,
  "bip125-replaceable": "no"
},

Hashgraph public ledger (51% attack)

I have some basic doubts about consensus algorithm like hashgraph. For instance, let’s take Raft the simplest leader based consensus algorithm, we cannot use it in a decentralised setting because it’s very easy for a single attacker to take control of the cluster by spinning thousands of nodes to support him.

“In summary, the voting based algorithm makes it very easy for the attacker whether its leader based or leaderless. So we cannot use it in a decentralised setting.”

Algos like PoW make its difficult for a single attacker to take over the network through the computational puzzle.

Taking about hashgraph it’s again a voting based algorithm, so wondering how it prevents a single attacker from getting control of the network in a decentralised setting (where you cannot trust your peers)???

I do understand how hashgraph works but wasn’t able to visualise it in a decentralised setting. Any insights? Thanks