Connection string issue in connecting to SQL Server

I am trying to connect my C# code to SQL Server.
My connection string is not working.

It gives the following error: "Format of the initialization string does not conform to specification starting at index 0."

I have checked my connection string multiple times, and have changed it different times.

string connectionString = "Data Source=Faizan; Initial Catalog=airports_sample; Integrated Security=True";

I have tried ., local, localhost, (local) and many other things.

I have checked SQL Server and the connection is open.
I have used Visual Studio Server Explorer to check the connection. It also says it is okay.

Any help would be really appreciated.