WCF question about sending result in xml format

I am new learning to create WCF web services. I created  this sample WCF service by taking help from different blogs online, it is working fine,  but I am not sure if it sends results in xml format or not. Please guide if I need to do something to send result in xml format.

Thanks.

GreetingService.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.Serialization;
using System.ServiceModel;


namespace Wcf.Samples.ServiceLibrary
{
    [DataContract]
    public class MyFaultException
    {
        private string _reason;
        [DataMember]
        public string Reason
        {
            get { return _reason; }
            set { _reason = value; }
        }
    }

    public class GreetingService : IGreeting
    {
        #region IGreeting Members

        public string Greet(string name)
        {
            return "Hello " + name;
        }

        public string Add(string num1, string num2)
        {
            int Result;
            try
            {
                int Number1 = Convert.ToInt32(num1);
                int Number2 = Convert.ToInt32(num2);
                Result = Number1 + Number2;               
            }
            catch (Exception exp)
            {
                MyFaultException theFault = new MyFaultException();
                theFault.Reason = "Error Occured: " + exp.Message.ToString();
                throw new FaultException<MyFaultException>(theFault);
            }
            return Result.ToString();
        }
        #endregion
    }
}

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IGreeting.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.ServiceModel;
using System.Runtime.Serialization;



namespace Wcf.Samples.ServiceLibrary
{
    [ServiceContract]   
    public interface IGreeting
    {
        [OperationContract]
        [FaultContract(typeof(MyFaultException))]
        string Greet(string name);

        [OperationContract]
        [FaultContract(typeof(MyFaultException))]
        string Add(string num1, string num2);
    }

}

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Service.svc

<%@ ServiceHost Language="C#" Debug="true" Service="Wcf.Samples.ServiceLibrary.GreetingService" %>

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Code on the client that invokes the service:

 protected void ButtonAdd_Click(object sender, EventArgs e)
    {
        GreetingClient client = new GreetingClient("WSHttpBinding_IGreeting");
        try
        {
            TextBoxResult.Text = client.Add(TextBoxNum1.Text, TextBoxNum2.Text);            
        }
        catch (FaultException<MyFaultException> ee) {TextBoxFault.Text = ee.Detail.Reason;}
        catch (InvalidOperationException ie) { TextBoxFault.Text = ie.Message; }
        catch (TimeoutException te) {TextBoxFault.Text = te.Message;}
        catch (FaultException fEx) {TextBoxFault.Text = fEx.Message;}
        catch (CommunicationException ce) { TextBoxFault.Text = ce.Message; }
        finally
        {
            client.Close();
        }
    }

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