Interoperability
You have different blockchain networks which operate independently, like Bitcoin, Ethereum, Sol etc. They operate on entirely different systems, you cannot send funds from the bitcoin network to Ethereum, you cannot draw up smart contracts that can be accepted on the different networks, most wallets cannot even hold Bitcoin and ethereum at the same time, you need designated wallets for each.
Interoperability is the ability of a blockchain to freely share information in a streamlined manner with other independent chains. You the user will not need to bounce back and forth to enjoy the benefits of the different networks. This is possible to an extent, but it cannot make it possible to send funds from one chain to another AFAIK.
Scalability
This is the ability of a network to cope with increasing users and demand while maintaining the level of service. If you have a restaurant that regularly cooks for 100 guests a night but then get a big break and boom, the guests starts going upwards, 250, 500, 1000+, their scalability will be their ability to cope with the increasing demand without a drop in quality of service.
In the blockchain it is normally used in relation to the ability of a network to cope with increasing transactions and get them confirmed in optimal time.
- Jay -