using System;

using System.Xml;

public class Program

{

    public static void Main()

    {

        var xml = @"<Block ID=""Ar0010100"" BOX=""185 211 825 278"" ELEMENT_TYPE=""h1"" SEQ_NO=""0"" />";

        var doc = new XmlDocument();

        doc.LoadXml(xml);

        XmlNodeList idList = doc.SelectNodes("/Block/@ID");

        foreach(XmlNode id in idList)

        {

            Console.WriteLine(id.Value);

        }

    }

}