using System;

using System.Xml.Serialization;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var pm = new P_M();

        pm.Cards = new List<string>();

        pm.Cards.Add("VISA");

        pm.Cards.Add("AMEX");

        pm.Cards.Add("DISCOVER");

        var x = new System.Xml.Serialization.XmlSerializer(pm.GetType());

        x.Serialize(Console.Out,  pm);

    }

}

​

public class P_M

{

    [XmlArray("Cards")]

    [XmlArrayItem(ElementName= "Card")]

    public List<string> Cards { get; set; }

}