Day-13 of learning Solana

So far, I have understood about -

1. The use of account and types of accounts used in Solana .
2. Difference in devnet, mainnet and testnet
3. How one can see details of any account present in Solana
4. What SOL and Lamports are.
5. About to read on-chain data in Solana
6. How account in Solana works similar to database in web2

Questions I have now -

1. What does on-chain data even mean and where does it live?
2. How much data at one transaction can be stored?
3. What is the logic behind transactions.
4. Why Proof of history is used as the consensus mechanism and why?
5. Is rent in Solana lesser as compare to gas fees in Ethereum and Polygon? If yes, then how and why?
6. How does the physical layer in Solana look like ?
7. Is the concept of bulk transaction used? If yes then how does it is handled?
8. Is the test done in devnet responds different than in testnet?
9. Can a wallet from other blockchain be used for transaction in Solana?
10. What is the best use case to use Solana?

Taking a day to explore these concepts so that I can answer these question in day 14 .