SerialNoEqualityComparer.cs

class SerialNoEqualityComparer : IEqualityComparer<Student>
  {
      public bool Equals(Student s1, Student s2)
      {
          if (s1 == null && s2 == null)
              return true;
          else if (s1 == null || s2 == null)
              return false;
          else if (s1.SerialNo == s2.SerialNo)
              return true;
          else
              return false;
      }

      public int GetHashCode(Student student)
      {
          return student.SerialNo.GetHashCode();
      }
  }