ZK

https://chain.link/education-hub/zero-knowledge-rollup

https://ethereum.org/en/developers/docs/scaling/zk-rollups/

Optimistic

https://ethereum.org/en/developers/docs/scaling/optimistic-rollups/

https://www.alchemy.com/overviews/optimistic-rollups

Comparative

https://www.coinbase.com/learn/tips-and-tutorials/what-is-the-difference-between-optimistic-rollups-and-zk-rollups

https://coinmarketcap.com/academy/article/optimistic-rollups-vs-zk-rollups-the-ultimate-comparison