// this will return the first correct answer,
// or throw an exception if there are no correct answers
var correct = answers.First(a => a.Correct);
// this will return the first correct answer,
// or null if there are no correct answers
var correct = answers.FirstOrDefault(a => a.Correct);
// this will return a list containing all answers which are correct,
// or an empty list if there are no correct answers
var allCorrect = answers.Where(a => a.Correct).ToList();

List<Model> newList = list.Where(m => m.application == "applicationname") .Select(m => new Model { application = m.application, users = m.users.Where(u => u.surname == "surname").ToList() }).ToList();