How can i Serialize c# keyword in Json string [duplicate]

what is best way to serialize below string in c# and How will i handle c# keyword "this" in this case.

{
 this: 
  {
   appId: "asd123dasfkioj240234kfwoe90fjiwcsskjf0"
  }
}

Or

{
    "this":
    {
            "appId":"asd123dasfkioj240234kfwoe90fjiwcsskjf0"
    }
}