Polkadot is a layer-0 protocol and multichain network founded by Dr. Gavin Wood, co-founder and former CTO of Ethereum. Polkadot provides security, scalability, and interoperability to a diverse ecosystem of use-case specific layer-1 blockchains and their dapps. Polkadot offers open governance, seamless upgradeability, energy efficiency, secure cross-chain interoperability, and more.
You can find the link to the block explorer below:
No (But can be done manually by validator or by a script)
Penalty
Yes if validator stops earning rewards for every block or era
If offline for a prolonged period the network will automatically "chill" the validator.
Chilling removes the validator from the active validator set and disqualifies them from the next election
Slashing
Yes with upto 100% penalty (equivocation or downtime)