Can you develop Windows Store app on Windows 7?

NO
only on Windows 8.

Top 10 Algorithms for Coding Interview

http://www.programcreek.com/2012/11/top-10-algorithms-for-coding-interview/

What is the way to avoid memory leak and faulted state when using block to call WCF client ?

DO NOT USE using block:

try
{
    client.Close();
}
catch (CommunicationException e)
{
    client.Abort();
}
catch (TimeoutException e)
{
    client.Abort();
}
catch (Exception e)
{
    client.Abort();
    throw; //Make sure to keep original exception 
}

http://msdn.microsoft.com/en-us/library/aa355056.aspx

JavaScript server side logging, JSNLog

http://jsnlog.com/

Null Object Pattern

Stopping checking if object is null

https://michaelfeathers.silvrback.com/when-it-s-okay-for-a-method-to-do-nothing
http://sourcemaking.com/refactoring/introduce-null-object