what difference between ref and out?

1.Explain about projects. 2.what is middleware 3.project structure 4.Authentication used in our project 5.Have you worked in project from scratch 6.Why used redis cache in storing token 7.advantages of microservices 8. what is request delegates 9.Write Code using linq , find frequency of each letter in input string 10.What is dependency injection 11.addScoped,AddTransient, AddSingleTon realtime example in your project 12.What are extension methods 13. Have you written custom extention methods 14.Do you know about Map(), run(),use() method, explain 15.Explain Asynchronous programing, async, await use 16.Shall we call async method without await? 17.What is thread and task 18.What is database triggers 19.find out sql query 1st three letters of your name in user table select query need to write 20.Difference between find() , firstOrDefault(), Single, SingleOrDefault() 21.Have you worked on versioning? 22.what is your team structure? how you work? direct client interaction? 23.What is fire-and-forget operations 25.How service bus queue works, explain