Update List without loop
https://stackoverflow.com/questions/19929316/updating-single-column-of-list-without-foreach-loop
As the Q of LINQ says, the basic usage of LINQ is to query, not to update.
The less verbose form of foreach is the ForEach method of List<T>:
li.ForEach(z => z.MarksExamTotalOverAll = 50);
List<Myclass> li = new List<Myclass>();
Parallel.ForEach(li, l => l.MarksExamOutOfMarksTotalOverAll = 50);