In case of Immediate query execution query is executed immediately or when we declare it, no matter whether collection is changed after it or not.
LINQ queries that return a singleton value are executed immediately. Some examples of singleton queries are Average, Count, First, and Max. These execute immediately because the query must produce a sequence to calculate the singleton result. You can also force immediate execution.
FollowingLINQ operators and extension methods supports immediate execution
// here query is executed immediately
Immediate execution doesn't provide the facility of query re-usability reason it produces result when we declare query.