Some helpful interview topics (Differences X VS Y)

IEnumrable VS IEnumarator 

IEnumrable VS IQueryable 

IEquatable VS IEqualityComparer VS IStructuralEquatable 
IComparable VS IComparer VS IStructuralComparable 

Delegates VS Events

Covariance vs ContraVaraince - http://www.c-sharpcorner.com/UploadFile/hasansheik/covariance-and-contravariance-in-C-Sharp/

Shadowing VS Overriding

Yield

Abstraction VS Encapsulation

Lambda expressions , Action , Func and Predicate

Generics

IOC & Dependancy Injection

async, await

MVVM, MVC, MVP

TPL

Indexer

Private Constructor

Private Class

Static Class VS Singleton
Culture and UICulture
LINQ: Single vs. First
a.Equals(b) and a == b?
SQL XML - CROSS APPLY V/S OUTER APPLY
Null values are in Sub query...
Diffrence Int32.parse, Convert.ToInt32, Int32.TryParse
Perform shallow copy of an object VS Deep Copy

Static Class VS Singleton

Static Class:-

1. You cannot create the instance of static class.
2. Loaded automatically by the .NET Framework common language runtime (CLR) when the program or namespace containing the class is loaded.
3. Static Class cannot have constructor.
4. We cannot pass the static class to method.
5. We cannot inherit Static class to another Static class in C#.
6. A class having all static methods.
7. Better performance (static methods are bonded on compile time)

Singleton:-

1. You can create one instance of the object and reuse it.
2. Singleton instance is created for the first time when the user requested.
3. Singleton class can have constructor.
4. You can create the object of singleton class and pass it to method.
5. Singleton class does not say any restriction of Inheritance.
6. We can dispose the objects of a singleton class but not of static class.
7. Methods can be overridden.
8. Can be lazy loaded when need (static classes are always loaded).
9. We can implement interface(static class can not implement interface).