One of the most frequently posed scenario based LINQ interview questions and answers, be ready for this conceptual question. You can retrieve a single element from a collection using a number of LINQ methods, including:   First(): Returns the collection's first element. An InvalidOperationException is thrown if the collection is empty.   Retrieves the first element of a collection using FirstOrDefault(). The type's default value is returned if the collection is empty.   Single(): Returns a collection's single element. An InvalidOperationException is thrown if the collection is empty or contains multiple elements.   Retrieves the single element in a collection using SingleOrDefault(). The type's default value is returned if the collection is empty. The collection throws an InvalidOperationException if it contains more than one entry.  Here are some examples of when each method would be appropriate:  First(): when you are sure that the collection has at least one element and you don't want to handle the exception if the collection is empty.  List students = ...
Student firstStudent = students.First();  FirstOrDefault(): when you are not sure that the collection has at least one element and you want to handle the case where the collection is empty.  List students = ...
Student firstStudent = students.FirstOrDefault();  Single(): when you are sure that the collection has exactly one element and you don't want to handle the exception if the collection is empty or has more than one element.  List students = ...
Student singleStudent = students.Single(s => s.Name == "John Doe");  SingleOrDefault(): when you are not sure that the collection has exactly one element and you want to handle the case where the collection is empty or has more than one element.  List students = ...
Student singleStudent = students.SingleOrDefault(s => s.Name == "John Doe");  In conclusion, LINQ has a number of methods, including First(), FirstOrDefault(), Single(), and SingleOrDefault, that let you extract a single element from a collection (). First() is used when you are certain that the collection has at least one element, FirstOrDefault() when you want to handle the case where the collection is empty, Single() when you are certain that the collection has exactly one element, and SingleOrDefault() when you want to handle the case where the collection is empty or has more than one element. Each of these methods is intended to handle a specific scenario.